4.5.3 For the assessment, it has been assumed that the Generating Equipment will operate for a worst case of 2,250 hours per year in the noise and air quality assessments, although actually running for 1,500 hours over an average of 5 years. In the noise assessment, it is assumed that the Generating Equipment will operate at night to represent the worst case scenario. Where there is the possibility that intermittent operation could give rise to more significant effects than continuous operation (for example start-up noise) this has been considered in the noise and air quality assessments, as well as disturbance to ecological receptors in the ecological assessment. This issue is not relevant to any other topic chapters.

4.6 Assessment Methodology

4.6.1 Methodologies for each subject area are presented within each of the technical chapters. These methodologies are based upon recognised good practice and guidelines specific to each subject area, and take into account any consultation responses relating to the methods used in the 2014 PEIR, the SoS Scoping Opinion and any additional requirements that have been identified in connection with the Project.

a) Assessment of Effects

4.6.2 The approach is broadly the same for all specialist topic areas with some variation in the descriptions of assessment criteria. For each topic, the assessment of significance will be informed by the sensitivity of the existing or baseline environmental conditions or character, and the magnitude of the change to the existing conditions or baseline character which occur as a result.

4.6.3 The determination of the significance of the likely environmental effects arising from development is a key stage in the EIA process. To assess the overall significance of an effect it is necessary to establish the magnitude of the effect occurring (i.e. the change to the existing baseline conditions as a result of the Project) and the sensitivity or importance of the receiving environment or receptor. Assessment of significance for environmental topics will combine professional judgement with the consideration of a number of factors including:

• The probability of the effect occurring based on the scale of certain, likely or unlikely;
• The sensitivity and value of the resource or receptor under consideration;
• The magnitude of the impact in relation to the degree of change which occurs as result (which includes the duration of the effect – short medium or long term);
• Reversibility of the effect;
• Comparison with legal requirements, policies and standards; and
• Comparison with applicable environmental thresholds.

4.6.4 The value of the receptors is assessed according to the relative importance of existing environmental features on or near to the site, or by the sensitivity of receptors i.e. whether they are likely to be robust enough to be unaffected by the

Prepared for: Abergelli Power Limited

AECOM 4-10