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Are Standard Design Features a Mitigation Measure in an Appropriate Assessment?

This High Court case concerned a proposed development in Trim, Co. Meath, which was to consist of 320 dwellings. Trim is designated as a heritage town and the site was close to a zone of archaeological potential and an architectural conservation area. There were several previous refusals of development on the site, for varied reasons. An Environmental Impact Assessment (EIA) screening report was prepared along with an ecological impact assessment which included proposed mitigation measures. An Appropriate Assessment (AA) screening report was also submitted which concluded that there would be no impact on the integrity of European Protected Habitats. An Bord Pleanála (the Board) granted permission in October 2020. Eco Advocacy CLG, a planning, environment and social justice registered charity, sought to challenge this.

Is a surface water drainage system a mitigation measure?

Eco Advocacy CLG raised questions of both domestic and EU law, including:

  • Alleged failure to address compliance with the development plan
  • Alleged failure to have regard to submissions
  • Alleged lack of reasons
  • Alleged unreasonableness of the decision

None of the domestic legal arguments succeeded.

The Judge, Mr Justice Humphreys, addressed the EIA and habitats issues at length in his judgment. The surface water run-off was to be collected below ground in storage tanks and be treated before outfalling to a stream around 100 metres south of the development.

He stated “the real question here is whether the surface water drainage system constitutes a mitigation measure or not to be regarded as such because it is simply a standard feature of the design that has nothing to do with the nearby European sites.”

The Court of Justice of the European Union (CJEU) has previously decided in a 2018 case that regard should not be had to mitigation measures at the screening stage of an Appropriate Assessment. That case established the principle that in order to determine whether it is necessary to subsequently carry out an assessment, it is not appropriate at the screening stage to take account of the measures intended to avoid or reduce the harmful effects of the plan or project on that site.

In deciding whether a measure is a “mitigation measures”, the Judge referenced previous applications of that judgment in an Irish context and stated he did not find it “quite as easy to reconcile the multitude of judgments as the board seems to suggest.” The main area of difference appears to be whether the measures are “intended” to reduce the impact on the site as opposed to whether they result in that “effect”. He found no clear and consistent line of authority on that point and on the meaning of the CJEU decision.

Another question arose as to whether it is relevant that the measures are standard practice or not. The Judge did not give this point much further consideration in the written judgment, stating “I certainly do not think that I can be totally confident that the Irish caselaw taken as a whole is completely clear and user-friendly as to what the [CJEU] decision means.”

Accordingly, the Judge has referred a question to the CJEU to provide clarity on this issue. Broadly, the Judge asked whether a competent authority is entitled to take account of project features that:

  1. Are not intended to reduce harmful effects on a European site even if they have that effect, and
  2. Would have been incorporated into the design as standard features

The Judge allowed the parties to make submissions on the proposed referral questions. In a subsequent decision ([2021] IEHC 610) he summarised the parties’ positions on the questions. In giving his preliminary views, the Judge agreed with the applicant and considered the “effect” rather than the “intention” to be the only objective criterion. He also noted that whether the measures are standard design measures is not relevant to that determination.


This judgment shows that there is no consensus on the approach to be taken on mitigation measures if they are incorporated into the design as standard rather than with the intention of reducing a harmful effect on a European site. We must await the CJEU response for further guidance on whether it is appropriate to distinguish a mitigation measure from other design features. In the meantime, a developer following a more cautious approach should consider whether it is possible to discount from its Appropriate Assessment screening report, any stand-alone design feature that will reduce a harmful effect on a European site.

Following the Judge’s preliminary views, a developer might want to treat a measure as a mitigation measure for the purposes of an AA screening assessment, even if the measure is not intended to have that effect or the measure is a standard design measure.

For more information, contact a member of our Planning & Environment team.

The content of this article is provided for information purposes only and does not constitute legal or other advice.

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