The EU Court of Justice has upheld arguments by opponents of a wind farm concerning the extent of the state agency, Coillte's, environmental responsibilities in relation to grid connection works for a windfarm in Co Laois.
The objectors case raised important issues concerning the extent of obligations under the EC Habitats Directive.
When referring the issues to the CJEU in March 2017, the High Court's Mr Justice Max Barrett noted the objectors argued the possible extinguishment of the Nore Freshwater Pearl Mussel, a species thought to be unique to Ireland and the River Nore region, "may be at stake".
The issues concerned whether mitigation measures, in the context of the requirements of Article 6.3 of the Directive, can be considered, as Coillte maintained, at the screening stage of a particular development or, as the objectors insisted, at the stage of an appropriate assessment.
In its judgment, the CJEU said Article 6.3 means, in order to decide whether it is necessary to carry out an appropriate assessment of the implications of a particular project for a protected site, the screening stage is not the appropriate stage to take account of measures intended to avoid or reduce harmful effects of the project.
A "full and precise" analysis of the measures capable of avoiding or reducing any significant effects on the relevant site must be carried out, not at the screening stage, but at the stage of the appropriate assessment, it said.
Taking account of such measures at the screening stage would be liable to "compromise" the practical effect of the Directive in general and the assessment stage in particular as the latter stage would be deprived of its purpose. There would be a risk of "circumvention" of that stage, which was "an essential safeguard" provided for by the Directive.
The assessment under Article 6.3 must have "complete, precise and definitive" findings and conclusions capable of removing all scientific doubt as to the effects of the proposed works on the relevant protected site, it said.
The CJEU added that persons such as these applicants have a right to participate in a procedure for adoption of a decision relating to an application for authorisation of a project likely to have a significant effect on the environment.
The case will now return to the High Court which will take the CJEU findings into account when deciding it.
The proceedings arose after Coillte got permission for eighteen wind turbines and associated development on lands at Cullenagh, close to the villages of Timahoe and Ballyroan.
People Over Wind and environmentalist Peter Sweetman, who had unsuccessfully opposed the permission, later challenged a July 2016 determination by Coillte, made under 2011 regulations giving effect to the Habitats Directive, that grid connection works to connect the windfarm to an ESB substation in Portlalaoise did not require a stage two appropriate assessment.
They argued such an assessment was required for reasons including the grid connection works, individually or with other plans or projects, are likely to have a significant effect on a European site.
They also claimed the mitigation measures proposed were not clearly defined and did not form part of an enforceable development consent.
Coillte argued its determination complies with the Directive and, given the outcome of a stage one screening assessment, there was no requirement for a stage two assessment.
It maintained protective measures applied at the design stage of a proposed development can be taken into account in the stage one assessment