Environmental Impact Assessment (EIA) is a critical process in the planning and development sector, designed to ensure that the likely significant environmental effects of development projects are understood and (where possible) addressed before planning permission is granted. Integral to sustainable development practices and aligned with the Institute of Environmental Management and Assessment (IEMA) principles, the EIA process considers factors such as biodiversity, water, air quality, and noise levels, among others.

The recent Dennis judgment, building on the principles established in the Hillside case, brings to light the complexities of integrating "severability" – put simply the capacity for parts of a planning permission to stand independently – into planning permissions, particularly for projects subject to EIA. These judgments, discussed further here, have important implications for the way practitioners approach the planning and development of large-scale projects, and specifically the use of “drop-in” applications.

The judgments underscore the legal and practical difficulties of ensuring that a project remains adaptable to future changes while also complying with the detailed requirements of EIA regulations. The notion of making a project severable to facilitate future amendments to elements of the development, in compliance with Hillside, introduces several challenges:

• EIA Scope and Integrity: The EIA process is predicated on assessing a defined project's environmental impacts. As has long been understood, EIA must ensure that the whole of a project has been assessed. Introducing the concept of severability complicates this assessment by introducing uncertainty about the project's final form and scope, potentially undermining the integrity of the EIA.
• Mitigation Measures and Monitoring: EIA often results in the identification of mitigation measures specific to the assessed development. If a project is made severable, ensuring the continuity and effectiveness of these measures across potentially independent phases or amendments becomes problematic.
• Public Participation and Transparency: A fundamental component of the EIA process is effective public participation, based on a clear understanding of the proposed development. Severability could affect this transparency, as the scope of the project may evolve significantly post-approval. At the very least, proper consideration of severability within a project may introduce multiple additional assessment scenarios leading to lengthy and complex reporting not readily accessible to the public (and indeed the planning authority).

Considering these factors, the practicalities of introducing severability into EIA projects in response to the Dennis and Hillside judgments are fraught with complexities. Achieving compliance with EIA regulations while maintaining the flexibility introduced by severability would require meticulous planning and risk assessment. The legal risks associated with attempting to navigate these complexities are considerable. Any failure to adhere to EIA requirements or to accurately represent the scope and scale of a severable project could lead to challenges, enforcement actions, and potentially significant project delays. The greater the level of severability sought, the greater the challenge and risk would become.

In summary, while the notion of severability emerging from recent case law may offer a means in theory to introduce flexibility into the planning and development process, achieving such flexibility without compromising compliance with EIA regulations is likely to be extremely difficult. Practitioners must tread carefully, considering the legal risks and the overarching aim of EIA to promote sustainable development practices.

Further information

Contact Ciaran Hagan or Charles McClea