How much is a lot? A systematic approach to impact significance assessment

Impact significance assessment is one of the most important, but also most difficult tasks in environmental impact assessment (EIA). However, assessment practices have varied, and the principles of assessment are not always communicated to the reader. This article presents an approach to assessing the significance of impacts developed in the IMPERIA project, and the experiences and opportunities for applying this approach. The IMPERIA project addressing essential issues The separation of essential and nonessential issues and an improved understanding of the scale of impacts are key objectives of environmental impact assessment. In order to understand the basics of assessment, systematic and illustrative methods are needed that rely on widely accepted principles of assessment. Otherwise, it is easy to end up in a situation where the most vociferous interest groups have the strongest impacts on public debate.The Nord Stream gas pipeline built in the Baltic Sea is a good example of a project where, before the EIA, the views presented in public debate were very far apart from each other. However, the information systematically produced in the EIA contributed to the public debate by aligning the views of different parties on the impacts. The IMPERIA project (LIFE11 ENV/FI/905), carried out in 2012–2015, has identified and developed tools and practices to support environmental impact assessment. The project sought to address a number of partly contradictory development objectives of the EIA process discussed in recent years; the evaluations should on the one hand be high quality, comprehensive, detailed and interactive, but on the other hand also focused on the essential aspects, sensitive to the key environmental risks and reasonable in terms of duration and cost. In this article, we present the most important output of IMPERIA project, i.e. the systematic assessment of impact significance using the developed ARVI approach. Significance assessment is a challenge to experts and laymen The IMPERIA project initially conducted an extensive survey of the international and Finnish literature on the topic. The main results of the survey can be summarized as follows: First, impact significance assessment is the central, but perhaps also the most difficult task of EIA. Secondly, there is no consensus on how significance should be assessed, which is partly because the practices and terminology have varied, both in Finland and abroad. Thirdly, the assessment of significance is always tied to values and is also open to interpretation. This is well illustrated by the following definition presented by the recognized EIA expert David Lawrence: “Significance determination in EIA [Environmental Impact Assessment] practice makes judgments about what is important, desirable or acceptable. It also interprets degrees of importance.” Fourthly, communication of the results of impact significance assessment and their basis is difficult because of the awkward terminology. Fifthly, EIA projects should focus on the most important impacts, because too often a large proportion of the resources are allocated a very detailed review of what are on the whole nonessential impacts. One of the objectives of an amendment to EIA Directive (2014/52/EU) that came into force in 2014 is to increase the effectiveness of the EIA process in decision-making on permits for projects. The aim is also to improve the cost-effectiveness of EIA procedures, which also involves highlighting the assessment of impact significance.