In essence appropriate assessment is an ecological assessment which deals with consequences of specific plan/project on specific habitats and species of a certain site. For this reasons each assessment is different and unique. However, it is an expert procedure and in its core are the data on which it is based and people that are doing it. The assessment has to be based on the good recent data and valid research, argumented and clear in its exposition and performed by the qualified experts with good understanding of ecology, the sites in question, as well as NATURA 2000 concept and national legislation.

European four-stage approach

A standard general methodology for the appropriate assessment procedure has been proposed and the EU level. The guidelines for the appropriate assessment have been prepared by the Oxford Brookes University, UK, and the European Commission and they are endorsed but not prescribed by the EC (Assessment of plans and projects significantly affecting NATURA 2000 sites).
The main aim of the four stage procedure is to ensure the right implementation of the article 6(3) and 6(4) of the Habitats Directive. However, underlying element of the staged concept is efficiency and rational use of time and funds meaning that it tries to ensure that assessment is not done when it is not necessary and that it deals only with relevant issues without excessive breadth which would lead to unnecessary delay and expenses on the side of proponents.

• Stage One: Screening — the process which identifies the likely impacts upon a Natura 2000 site of a project or plan, either alone or in combination with other projects or plans, and considers whether these impacts are likely to be significant. All projects that have no potential significant impact to Natura 2000 complete the assessment at this point and may proceed to approval procedures.
  
  
• Stage Two: Appropriate assessment - the consideration of the impact of the project or plan on the integrity of the Natura 2000 site of the project or plan, either alone or in combination with other projects or plans (present or planned), with respect to the site’s structure and function and its target features. Additionally, where there are adverse impacts, an assessment of the potential mitigation of those impacts is performed.
  In this stage of appropriate assessment the proponent submits the document or study which analyses the effects of a given project/plan on the NATURA 2000 sites. The size of the document is not prescribed meaning that it can have only few pages for some small projects or even several hundreds of pages for big ones, all depending on the nature of the project, its potential impacts and the number of sites likely to be affected. However, content of the document has to be complete which means it has contain all the data prescribed in the Ordinance on nature impact assessment (NN 89/07).

• Stage Three: Assessment of alternative solutions — the process which examines alternative ways of achieving the objectives of the project or plan that avoid adverse impacts on the integrity of the Natura 2000 site; If the significant impact remains the proponent should explore other feasible alternative solutions to achieve the goal including the zero option of doing nothing. Alternative solutions that are proposed should be returned to stage 2 for assessment.

• Stage Four: Compensation measures - Assessment where no alternative solutions exist and where adverse impacts remain — an assessment of compensatory measures where, in the light of an assessment of imperative reasons of overriding public interest (IROPI), it is deemed that the project or plan should proceed.
  At this stage it is determined that if the project is necessary for imperative reasons of the overriding public interest than the project may be approved in spite of negative results of the appropriate assessment. However, coherence of the Natura 2000 has to be ensured through compensatory measures by i.e. recreating lost habitats elsewhere on the site or adding similar areas to NATURA 2000. There are strict compensation rules regarding equivalence and timing of compensatory measures that should be adhered to.

It is understood from case law that imperative reasons of public interest have to be sufficiently strong to really override importance of preservation of NATURA 2000 sites meaning that they should be long term, aimed to protection of fundamental values (health, safety, environment), part of the fundamental policy of the State and society, or related to fulfilling economical or social needs related to obligations of public service at the national or international scale.