4. Environmental Impact Assessment Methodology

Environmental Impact Assessment Methodology

4.1. Introduction

  1. This section presents the methodology that will be applied to the Array Environmental Impact Assessment (EIA) Report. The methodology for the identification and assessment of likely significant environmental effects, as defined in the EIA Regulations (The Marine Works (Environmental Impact Assessment) Regulations 2007; see Appendix 4), is discussed in this section, alongside the proposed methodology for the identification and assessment of cumulative and inter-related impacts, including consideration of potential transboundary effects. The methodology will follow a systematic and auditable evidence-based approach to assess and interpret the potential effects on physical, biological and human receptors within the offshore environment.

4.2. Basis of Assessment

4.2.1. EIA Legislative Basis and Guidance Documents

  1. In order to comply with applicable law and policy (see Appendix 4) and in particular with the Marine Works (Environmental Impact Assessment) Regulations 2007 and the Electricity Works (Environmental Impact Assessment) (Scotland) Regulations 2017, an EIA Report will be prepared when applying for Section 36 consent and marine licence(s) for the Array, as discussed within section 1.5 and Appendix 4. A separate EIA Scoping Report and EIA Report will be produced for the Proposed offshore export cable corridor(s). In addition, a separate EIA Scoping Report and EIA Report will be prepared for the planning permission application(s) for the Proposed onshore export cable corridor(s) and associated infrastructure (above MLWS).
  2. The following Regulations will also be considered in the production of the Array EIA Report, in addition to the EIA Regulations described in section 1.5 and Appendix 4:
  • the Conservation of Habitats and Species Regulations 2017; and
  • the Conservation of Offshore Marine Habitats and Species Regulations 2017 (which apply to marine licences and Section 36 applications within the Scottish Offshore region).
  1. Guidance and good practice documents have also been developed, in addition to the legislative requirements, to assist with the production of a ‘fit for purpose’ EIA. These include:
  • Marine Scotland Consenting and Licensing Guidance: For Offshore Wind, Wave and Tidal Energy Applications[4] (Marine Scotland, 2018);
  • Guidelines for Ecological Impact Assessment (EcIA) in the UK and Ireland – Terrestrial, Freshwater, Coastal and Marine (Chartered Institute of Ecology and Environmental Management (CIEEM), 2022);
  • Environmental Impact Assessment for offshore renewable energy projects (British Standards Institute (BSI), 2015);
  • Guidelines for data acquisition to support marine environmental assessments of offshore renewable energy projects (Centre for Environment, Fisheries and Aquaculture Science (Cefas), 2012);
  • A Review of Assessment Methodologies for Offshore Wind Farms (Collaborative Offshore Wind Research into The Environment (COWRIE) METH-08-08) (Maclean et al., 2009);
  • Institute of Environmental Management and Assessment (IEMA) Environmental Impact Assessment Guide to Shaping Quality Development (IEMA, 2015);
  • Planning Advice Note (PAN) 1/2013 Environmental Impact Assessment (Scottish Government, 2013);
  • A Handbook on Environmental Impact Assessment (NatureScot, 2018);
  • Advice Note Seventeen: Cumulative effects assessment relevant to nationally significant infrastructure projects (The Planning Inspectorate, 2019); and
  • Cumulative Impact Assessment Guidelines - Guiding Principles for Cumulative Impact Assessment in Offshore Wind Farms (RenewableUK, 2013).
  1. It should also be noted that there are a number of guidance documents which are in the process of being issued or consulted on by NatureScot and MS-LOT in the near future. The Applicant will monitor for, review, and endeavour to adhere to new guidance, where relevant, in the Array EIA Report.

4.2.2. The Environmental Impact Assessment Process

  1. The EIA process broadly consists of:
  • EIA Screening: The Applicant assesses whether an EIA is required for the Array, based on the thresholds and criteria of the project against the Schedules within the EIA Regulations. The Array is considered a Schedule 2 project as it is classed as an “Installation for the harnessing of wind power for energy production (wind farm)” (HM Government, 2007). The Applicant can submit a request for a Screening Opinion from the Scottish Ministers, however, the Applicant has chosen to voluntarily prepare an EIA Scoping Report and EIA Report for the Array without a Screening Opinion following the steps below;
  • EIA Scoping: The Applicant produces an Offshore EIA Scoping Report for the Array (this document) and requests a formal Scoping Opinion from Scottish Ministers;
  • Consultation: The Applicant will undertake stakeholder engagement during the pre-application period;
  • EIA Report preparation: The Array EIA Report will be prepared. This will consider the responses to the consultation process and the outcomes of the assessment of the likely significant effects (as defined in EIA Regulations (see section 1.5) of the Array during the construction, operation and maintenance, and decommissioning stages of the project lifecycle;
  • EIA Report consultation: The Applicant is required to publicise the Array EIA Report (and the application to which it relates) to allow the consultation bodies and the public to be given the opportunity to provide their views about the Array EIA Report, including the project design;
  • Determination: The competent authority is required to examine all the environmental information, including the Array EIA Report, as well as any comments and representations received from consultation bodies and the public, to enable them to reach a reasoned conclusion on the significant effects of the Array on the environment. The competent authority must consider the environmental information and the conclusions reached, and whether any monitoring measures are appropriate when making the decision whether or not to give consent for the Array; and
  • Decision notice: The competent authority is required to inform the public and the consultation bodies of the decision and must publish a ‘decision notice’ incorporating the authority’s reasoned conclusion on the significant effects of the development on the environment.
  1. Figure 4.1   Open ▸ provides an overview of the Section 36 and marine licensing process and illustrates how the EIA Scoping stage fits within this process.

Figure 4.1:
Stages of the Licensing Process in Scottish Waters

Figure 4.1: Stages of the Licensing Process in Scottish Waters


4.3. Key Principles of the EIA

4.3.1. Overview

  1. Within the Array EIA Report, each topic will consider the following:
  • identification of the study area for the topic-specific assessments;
  • description of the planning policy and guidance context;
  • summary of consultation activity, including comments received in the Array Scoping Opinion and all other engagement undertaken during the pre-application phase;
  • description of the environmental baseline conditions; and
  • presentation of impact assessment, which includes:

           identification of the MDS for each impact assessment;

           a description of the mitigation and design measures implemented as part of the Array which aim to prevent, reduce or offset environmental effects;

           identification of likely impacts and assessment of the significance of identified effects, considering any measures implemented as part of the Array;

           identification of any secondary mitigation measures (IEMA, 2016) required regarding likely significant effects (as defined by the EIA Regulations and in addition to mitigation measures implemented as part of the Array), alongside a consideration of any residual effects;

           identification of any future monitoring required;

           Cumulative Effects Assessment (CEA) with any other developments, including those that are proposed, consented and under construction, and projects, plans or activities that are currently operational that were not operational when baseline data was collected (if applicable); and

           transboundary effects assessment for any potential transboundary effects on European Economic Area (EEA) states.

  1. A separate standalone section will assess inter-related effects (i.e. inter-relationships between environmental topic areas). This section will include a receptor based inter-related effects assessment of the Array on each of the identified receptor groups, as well as an ecosystem-based assessment which will provide a qualitative assessment of the impacts of the Array at the ecosystem level to assess any effects on predator – prey relationships and the functioning of the ecosystem.
  2. A number of key principles will be applied within each topic section. These are detailed in sections 4.3.2 to 4.3.8 below.

4.3.2. Proportionate EIA

  1. This Scoping Report has been developed using a number of tools and processes with the aim of producing a proportionate EIA Report for the Array (as per IEMA (2017), and the Industry Evidence Programme (IEP) (Crown Estate et al., 2018)). These tools and processes will also be applied within the Array EIA Report.
  2. Figure 4.2   Open ▸ presents the general approach taken for proportionate EIA in this Scoping Report.


Figure 4.2:
Proposed Proportionate EIA Process Used Within this Scoping Report and the Subsequent Array EIA Report

Figure 4.2: Proposed Proportionate EIA Process Used Within this Scoping Report and the Subsequent Array EIA Report

  1. The tools and processes noted in paragraph 153 include the following:
  • development of a draft Stakeholder Engagement Plan;
  • application of the existing evidence basis; and
  • commitment to designed in measures.

                        Draft Stakeholder Engagement Plan

  1. The dSEP has been developed to enable engagement throughout the pre-application phase (see Appendix 1).
  2. The purpose of the dSEP is to allow stakeholders to plan resources to ensure post-scoping consultation is focused, direct and progresses in an efficient manner.
  3. As noted in paragraph 176, pre-Scoping workshops were held with key stakeholders in November 2022 to present the baseline characterisation and data sources for a range of topics. Feedback and points of agreement from these workshops have been considered and presented within this Scoping Report for the relevant sections. Further information on these workshops can be found in paragraph 176 and Appendix 1.
  4. Post-Scoping consultation will be used to discuss development and agreement of modelling methodologies to be used, interpretation of significance, application of new guidance, and/or agreeing the level of technical assessment which will be presented for impacts within the Array EIA Report. This will ensure that the Array EIA submission documents will be focused on likely significant effects (as defined by the EIA Regulations). The dSEP is considered a ‘live’ document which will be reviewed and updated in response to feedback from stakeholders as part of their Scoping representations.
  5. At the time of writing this Scoping Report, the following topics have been identified in the dSEP as requiring focused post-Scoping consultation, subject to scoping feedback:
  • benthic subtidal ecology (post-Scoping consultation expected to be minimal);
  • fish and shellfish ecology;
  • subsea noise and marine mammal ecology;
  • offshore ornithology;
  • commercial fisheries; and
  • shipping and navigation.
  1. In addition, there may be the need to discuss the approach to CEA and any queries raising from soon to be published guidance which may affect the approach taken in the Array EIA Report.
  2. The section labelled “next steps” within each topic section of this Scoping Report, details the proposed approach for post-Scoping stakeholder engagement in line with the appended dSEP (see Appendix 1).

                        Existing evidence basis

  1. As noted in section 3, the site boundary was subject to an extensive site assessment process through the development of the SMP, followed by the Applicant’s site assessment process pre-ScotWind award. This existing baseline data and site-specific information has been drawn upon to inform this Scoping Report and the subsequent Array EIA Report. In addition, site-specific information from Berwick Bank Offshore Wind Farm and other Scottish offshore wind farms in the vicinity of Ossian has been considered as part of the pre-ScotWind award site assessment process undertaken by the Applicant, as well as preliminary site-specific survey data for the Ossian site boundary, including digital aerial survey data, and geophysical and environmental survey data. Each technical section of this Scoping Report includes a detailed desktop review which aims to:
  • provide an initial high-level summary of the baseline environment;
  • provide an overview of the existing data to support the Array EIA Report;
  • provide rationale for scoping out of impacts from the Array EIA Report where there is clear evidence to do so (e.g. lack of a receptor-impact pathway); and
  • provide the existing evidence base to support scoping in of impacts to the Array EIA Report, where appropriate.
  1. Offshore digital aerial surveys for ornithology and marine mammals were completed between March 2021 and February 2023. Metocean surveys are ongoing (due to be completed in August 2023), and geotechnical surveys are planned to commence in late Q1 2023 which will further inform the Array EIA Report and final project design.

                        Designed in measures and mitigation measures

  1. There are three different forms of mitigation including:
  • Primary mitigation (inherent): “Modification to the location or design of the development made during the pre-application phase that are an inherent part of the project, and do not require additional action to be taken” (IEMA, 2016).
  • Secondary mitigation (foreseeable): “Actions that will require further activity in order to achieve the anticipated outcome. These may be imposed as part of the planning consent, or through inclusion in the ES” (IEMA, 2016).
  • Tertiary mitigation (inexorable): “Actions that would occur with or without input from the EIA feeding into the design process. These include actions that will be undertaken to meet other existing legislative requirement, or actions that are considered to be standard practices used to manage commonly occurring environmental effects” (IEMA, 2016).
Designed in measures (primary and tertiary mitigation)
  1. The term ‘designed in measures’ has been used to refer to primary and tertiary mitigation within this Scoping Report. The design of the Array has been informed via this iterative approach to the environmental impact assessment process, through the identification of likely significant effects (as defined by the EIA Regulations) and development of designed in measures to address these. Through the incorporation of designed in measures, the Applicant’s commitment to implementing the identified measures is demonstrated. These are referred to as designed in measures throughout this Scoping Report and the subsequent Array EIA Report.
  2. This approach ensures that the significance of effect presented in throughout this Scoping Report and the subsequent Array EIA Report represents the maximum residual effect that the Array will have, should the application for consent be approved and the Array be constructed.
  3. Both primary and tertiary mitigation measures are considered as designed in measures as they are incorporated as part of the project design. Therefore, the Environmental Impact Assessment (EIA) can be undertaken assuming that these designed in measures will be implemented during the relevant project phase. As a result, potential effects which might arise prior to the implementation of designed in measures do not need to be identified as potential effects as there is no potential for them to arise (IEMA, 2016). It should be noted that in each topic specific section of this Scoping Report, a full list of potential impacts without application of designed in measures has been presented, alongside a refined list of impacts proposed to be scoped in and out of the Array EIA Report after application of designed in measures. The topic specific designed in measures are presented in each topic receptor section.
  4. Section 2.7 presents all designed in measures considered in this Scoping Report. The development of mitigation measures will continue as the EIA progresses and in response to stakeholder engagement. An iterative process will be used for any additional measures and the dSEP will be updated (Appendix 1).
Secondary mitigation
  1. Secondary mitigation is a flexible form of mitigation that can be proposed at any point within the EIA process, including during the decision-making process (IEMA, 2016). As noted above, this form of mitigation requires further activity, particularly at the post-consent stage. Therefore, secondary mitigation measures are additional measures applied after completion of the assessment process to prevent, reduce and offset likely significant effects (as defined by the EIA Regulations) which could not be avoided through designed in measures.

4.3.3. Design Envelope Approach and Maximum Design Scenario

  1. In accordance with current good practice and the “Rochdale Envelope Principle[5]”, the assessment of the Array will utilise the PDE approach (also known as the Rochdale Envelope approach). The PDE concept allows for some flexibility in final project design options within a maximum design, where the full details of a project are not necessarily known when the application is submitted.
  2. The PDE parameters are set out in section 2, where the maximum project design values for relevant components of the Array are identified. The PDE considered will be the scenario which would give rise to the greatest potential impact (hereafter referred to as the MDS) for each of the topic sections within the Array EIA Report, and for each of the impacts assessed.
  3. The Applicant has undertaken a process of PDE refinement prior to submission of this Scoping Report. Therefore, the assessment which is presented in the final application will be based on a PDE which is as refined and focused as is practical whilst still retaining a degree of flexibility for new technology or design solutions in the post-consent phase.

4.3.4. Consultation and Stakeholder Engagement


  1. Appendix 4, section 4.5.2 notes that there is no legislative basis for undertaking Pre-application Consultation (PAC) as the Array application is located in Scottish offshore waters (12 nm to 200 nm), however, the PAC Regulations are considered good practice for undertaking public engagement.
  2. An overview of consultation undertaken to date is presented in Appendix 1. Paragraphs 176 to 182 outline the Applicant’s proposed approach to stakeholder engagement to be followed during the pre-application period.

                        Engagement to date

  1. Pre-Scoping stakeholder engagement has been undertaken to support the development of this Scoping Report. Consultation has included general project introductions to key stakeholders and regulators; discussions on proposed survey methodologies; pre-scoping engagement on the Array; interim updates with key Statutory Nature Conservation Bodies (SNCBs) and stakeholders, and updates on interim data results for topics such as ornithology, commercial fisheries and shipping and navigation. In addition, the Applicant held pre-Scoping workshops with SNCBs in November 2022 to present the approach to scoping of the Array and to gain feedback on the scoping in/out of specific impacts to key receptors. Topics covered in the workshops included physical processes, benthic ecology, fish and shellfish ecology, marine mammal ecology and subsea noise, offshore ornithology, seascape, landscape and visual resources and cultural heritage, shipping and navigation, and commercial fisheries.
  2. An overview of the stakeholders engaged with to date is provided below:
  • NatureScot;
  • MS-LOT;
  • Marine Scotland Science (MSS);
  • Royal Society for the Protection of Birds (RSPB);
  • Maritime Coastal Agency (MCA);
  • Northern Lighthouse Board (NLB);
  • North and East Coast Regional Inshore Fisheries Group (NECRIFG);
  • Scottish Fishermen's Federation (SFF); and
  • Scottish White Fish Producers Association (SWFPA).

                        Future engagement

Array Scoping
  1. Once this Scoping Report has been received by the Scottish Ministers, they will consult with statutory consultees, in accordance with the EIA Regulations. This consultation is required to obtain advice and feedback from each consultee or advisor on the potential effects which should be scoped in or out of the EIA. A Marine Scotland gap analysis will be developed based on the Array Scoping Opinion to record the identified environmental concerns and will be used to inform the Array EIA Report preparation.
Pre-Application Consultation event
  1. The PAC Regulations apply where activity is planned within Scottish territorial waters and require Applicants for a ‘prescribed class’ of activity to notify the MCA, NLB, NatureScot, and any delegate for a relevant marine region. The Array is located within Scottish offshore waters, therefore, there is no requirement under the PAC Regulations for the Applicant to notify delegates about the proposed activities within the Array. However, the Applicant proposes to follow the principles of the PAC Regulations for the Array as these Regulations are considered good practice for undertaking public engagement.
  2. The Applicant proposes to hold at least one pre-application event, for example, in the form of a public exhibition, where these bodies, other stakeholders, and members of the public may engage with and provide comments to the Applicant. It is proposed that this public exhibition event is held in 2023 and further details of this event will be advertised.
  3. Where appropriate to do so and if sufficient information on the grid connection and onshore elements of the project are available, public consultation will be carried out for the onshore and offshore elements at the same event, in order to give third parties a full understanding of the whole project.
Additional stakeholder engagement
  1. Consultation with key statutory and non-statutory stakeholders throughout the pre-application process will continue as set out in the dSEP (Appendix 1) and on agreement with stakeholders. The Array EIA Report will provide a summary of key consultation undertaken, including the outcomes of the public exhibition.

4.3.5. Impacts and Effects

  1. A range of impacts and effects regarding the physical, biological and human environment, for offshore receptors, have the potential to arise from the Array infrastructure and activities. Where a change is caused by an action, this is defined as an ‘impact’, for the purposes of the Array EIA Report. For example, the installation of moorings and anchoring systems (action) is likely to result in temporary and/or long term seabed loss and disturbance (impact). Impacts may be direct, indirect, temporary, irreversible, secondary, cumulative and inter-related, and can also be either positive or negative. However, the relationship between them can be complex.
  2. The consequence of an impact is defined using the term ‘effect’. Further elaborating on the example presented above, the installation of moorings and anchoring systems (action) results in temporary and/or long term seabed loss (impact), which may have the potential to disturb benthic habitats and lead to mortality or injury of benthic species (effect). The significance of effects is defined by considering both the magnitude of impact and the sensitivity of each receptor/receptor group.
  3. The extent, duration, frequency and reversibility of an impact are considered when determining the magnitude of an impact. For the purposes of the Array EIA Report, the physical or biological resource, or user group that may be affected by the potential impacts are defined as ‘receptors’. When determining the sensitivity of each receptor/receptor group, a number of factors may be considered, including the vulnerability, recoverability and value/importance of the receptor.
  4. A matrix approach will be applied in the Array EIA Report to ensure a consistent approach is taken when defining the significance of an effect ( Table 4.1   Open ▸ ). Where a range is suggested for the significance of effect, for example, minor to moderate, it is possible that this may span the significance threshold. The technical specialist’s professional judgement will be applied to determine which outcome defines the most likely effect, which takes in to account the sensitivity of the receptor and the magnitude of impact. The technical specialist will provide an explanation for this determination in the relevant section of the Array EIA Report where applicable.


Table 4.1:
Matrix Used for the Assessment of the Significance of the Effect

Table 4.1: Matrix Used for the Assessment of the Significance of the Effect


                        Approach to assessment of significance

  1. Within the Array EIA Report, effects will be assessed as ‘significant’ or ‘non-significant’. A significant effect is defined as a level of effect of equal to or greater than ‘moderate’. A non-significant effect is considered as a level of effect of ‘minor’ or less. In the decision-making process, effects of moderate significance or above are considered important, whereas effects of minor significance or less are considered to have little, if any, importance.
  2. The general approach described in the Design Manual for Roads and Bridges (DMRB) (Highways England et al., 2019) and Environmental Impact Assessment for Offshore Renewable Energy Projects – Guide (BSI, 2015) has been considered as part of this matrix approach. However, several modifications have been made with regard to proportionality, including:
  • where a magnitude of impact is determined as ‘no change’ no assessment will be undertaken since it will always lead to a non-significant effect;
  • where a magnitude of impact is determined as ‘negligible’, this will not be considered further as it will always lead to a non-significant effect, even if more than one negligible magnitude impact was being considered cumulatively; and
  • where it is determined that a receptor or receptor group has negligible importance, value or sensitivity, this will not be considered further as it will always lead to a non-significant effect.
  1. The Array EIA Report will follow a “feedback loop” methodology, as shown in Figure 4.3   Open ▸ . Using this methodology, an impact is initially assessed to determine the significance of the environmental effect. If the effect of an impact is initially determined to have a major significant adverse outcome, primary and tertiary mitigation will be applied in order to reduce or offset the magnitude of impact, for example, through changes to the Array design parameters. Secondary mitigation such as engineering controls or construction methods will be employed, where possible, if the effect of an impact is initially determined to have a moderately significant adverse outcome, again, to reduce or offset the magnitude of the impact.
  2. As illustrated within Figure 4.3   Open ▸ , the EIA practitioner will repeat this process until they are content that:
  • the effect is reduced to a level that is not significant in EIA terms; or
  • no further changes can be made to the Array design parameters to reduce the magnitude of impact and the significance of the effect. An overall effect that is still significant in EIA terms may be presented in these instances.
  1. Using this iterative approach, it can be presumed that the significance of effect presented for each identified impact is representative of the maximum residual adverse effect the Array may have on the receiving environment.
  2. Appendix 2 presents all designed in measures considered in this Scoping Report. The development of mitigation measures will continue as the EIA progresses and in response to stakeholder engagement. An iterative process will be used for any additional measures and the dSEP will be updated (Appendix 1).

4.3.7. Cumulative Effects Assessment


  1. Under the EIA Regulations, a CEA is legally required. The CEA considers the impacts arising from the Array alone as well as cumulatively with other relevant plans, projects and activities, and can be defined as the combined effect of the Array in combination with the effects from a number of different projects, on the same receptor or resource.
  2. The CEA is essential to identify foreseeable developments or activities with which the Array may interact, resulting in cumulative impact. Cumulative impacts may arise from all phases (construction, operation and maintenance, and decommissioning) of the Array.
  3. The Marine Scotland (2018) Consenting and Licensing Guidance: For Offshore Wind, Wave and Tidal energy Applications states that “Engagement with MS-LOT is required to identify which plans/projects/on-going activities should be included in the in-combination element of the cumulative effects assessment (CEA)”’. The CEA will consider offshore wind projects in the east of Scotland region, and other developments including those which are:
  • already constructed;
  • under construction;
  • permitted application(s) not yet determined; and
  • plans and projects which are “reasonably foreseeable” (i.e. developments that are being planned, including, for example, offshore renewable energy project which have a CES Option to Lease Agreement or Crown Estate equivalent, offshore renewable energy projects that have been scoped).
  1. In addition, the Proposed offshore export cable corridor(s) and Proposed onshore export cable corridor(s) (including the onshore substation at the Proposed landfall location(s)) will be considered within the CEA, as well as other ScotWind projects located in the vicinity of the Array which fall into the criteria listed above.