IEMA – Implementing the mitigation hierarchy from concept to construction

With almost a decade having passed since IEMA’s guidance on ‘ Shaping Quality Development’ (2015) and its guidance on ‘Delivering Quality Development’(2016), it is important to take stock of the contemporary state of EIA and SEA practice and the influence the process has in creating sustainable development. IEMA seeks to do this through the recent delivery of its newest guidance ‘Implementing the Mitigation Hierarchy from Concept to Construction’ (2024). This guidance now supersedes the previous guidance listed above, however, it is built upon its foundations whilst expanding its position towards implementing mitigation within EIA. Furthermore, this guidance is written in a manner that attempts to secure the inclusion of mitigation for potential changes to the structure of environmental assessment, noting the recent uptick in interest surrounding Environmental Outcomes Reporting (EORs).

When compared to its predecessors, this updated guidance helps to create a pathway towards strengthening the level of integration of mitigation measures into EIA through a variety of means over the lifetime of a project, however, its overarching idea remains the same as previous guidance: For the most effective mitigation, measures should be embedded into the project as early as possible rather than hastily or generically crafted as issues emerge throughout the EIA process. Through early assessment, conversations and involvement between environmental and design teams, ensuring mitigation is practical, easier to implement and enforceable, through increased monitoring. When involved in these early conversations informed by assessments looking at microclimate, acoustics, habitat retention / BNG for example, the Temple team have been able to recommend sustainable design changes earlier within the development’s lifespan influencing the layout of an urban development to minimise environmental effects.

As noted by IEMA, one of the principal goals of impact assessment is ‘to identify the proposal’s likely significant effects and for the significant effects, seek to initially avoid or prevent them. Where adverse effects are unavoidable, mitigation measures should be developed to reduce and minimise these effects.’  The forms of mitigation measures incorporated into a project throughout its lifetime fall under IEMA’s mitigation hierarchy, as shown in Figure 1.

Figure 1 – The Mitigation Hierarchy (IEMA, 2024)

The Temple team has proven experience delivering these forms of mitigation through early involvement. In this case, we have altered the project design to either fully avoid or prevent significant environmental effects for a fraction of what this would cost at later stages. Under the new guidance, Temple will still incorporate mitigation into the design of all projects we work on to create meaningful, sustainable development. Figure 2 below provides the benefits of early project involvement when utilised effectively by developers.

Figure 2 – Benefits of Early Project Involvement

Starn, K. (2019). Become a Carbon Hero with Five Easy Tactics. Steven Winter Associates, Inc. Retrieved from link.

This guidance furthermore calls for the separation of enhancement from the mitigation hierarchy (shown in Figure 1), noting that ‘project proponents cannot necessarily be forced to pursue enhancement as a goal through the EIA process’. While not necessarily creating seeking enhancement through the EIA process, this strategy is meant to feed into and fulfil other policy requirements for large-scale property development, including the Five-Yearly Plan introduced through the Environment Act 2021, Biodiversity Net Gain Requirements and the Public Services (Social Value) Act 2012. For some environmental topics, enhancement may only be possible if the effects are avoided. For example, enhancement for pollution-based topics inherently assumes that pollution levels are being improved, rather than degraded, by a development. It is hard to justify any additional measures to improve air or water quality being considered an ‘enhancement’ if the development would otherwise lead to a reduction of air or water quality, even if this is not found by an environmental assessment to be substantive.

On the other hand, for some topics it is possible for (particularly temporary) adverse effects to be identified, requiring mitigation that does not quite achieve the definition of avoidance, but further enhancement is possible to result in something that is in the round a net benefit. An example of this might be necessary vegetation removal affecting nesting birds in a development, where mitigation would typically involve timing works outside of the nesting bird season, but where additional trees, shrubs and other vegetation may then be created as part of a habitat. In such instances, the separation of enhancement from the mitigation hierarchy can be better understood.

As such, Temple’s methodology behind the inclusion of enhancement first and foremost within our mitigation strategy, shown below in Figure 3, is still in line with best practice measures for EIA, with environmental receptors that could potentially be strengthened through a proposed development always considered before any other form of mitigation.

Figure 3: Temple’s Mitigation Hierarchy