Archived Documents:

Accumulating Environmental Impacts: GOMMMS Supplement

1. This should be read in conjunction with the DETR publication 'Guidance on Methodology for Multi-Modal Studies' (GOMMMS) dated March 2000.

2. This guidance supplements that given in GOMMMS for the assessment of impact on landscape, townscape, heritage, biodiversity and the water environment. It clarifies the approach to be adopted for these sub-criteria in circumstances where a number of key environmental resources are affected by an option.

3. This guidance has been discussed and agreed with the environmental statutory bodies (Countryside Agency, English Nature, English Heritage and the Environment Agency).

GOMMMS, Volume 2, Sections 4.6 - Environmental capital approach

1. Advice in GOMMMS on the accumulation of environmental impacts is variable across the five sub-criteria. The advice given in this supplement is based on that given in GOMMMS for biodiversity and the water environment. It is intended to provide a systematic basis for accumulating site or location specific results, while also allowing for the exercise of expert judgement.

2. Many multi-modal studies will affect quite large geographical areas. Inevitably, key environmental resources will vary across these large study areas. For example:

• there may be areas of archaeological importance in one part of the study area, and historic buildings in another
• woodland may be a key biodiversity feature in one location, with wetland being key elsewhere
• there may be several towns or cities in a study area, each with different townscape characteristics

3. Further variation is likely to arise because the nature of options (and hence their impact) may vary across the study area. For example, one part of the study area may be affected by proposals for a guided busway, while a road scheme may be proposed elsewhere.

4. These variations may be addressed by treating each key environmental resource separately. Key environmental resources should be identified on the basis of the coherence of character within each resource and the distinctiveness of character between resources. It is likely that the geographical scale of the resources will vary between impact types. For example, key landscape resources will often be large geographic areas, while key biodiversity resources may be quite small. Excessive detail should be avoided the level of detail should be no more than is needed for robust decisions to be taken.

5. Identifying key environmental resources in this way enables the nature of the resource to be concisely described using the environmental capital approach. It also allows the impact of that element of the option relevant to the resource to be clearly stated. Together, these allow the significance of the impact on each resource to be assessed relatively easily, using the guidance provided in GOMMMS. The results of this process should be an assessment on the standard seven point scale for each key environmental resource.

6. These separate assessments must be combined to prove an overall assessment for the option as a whole, suitable for use in the appraisal summary table (AST). The procedure to be adopted for this is discussed below. It is intended to provide a transparent and systematic basis for accumulating results, while also allowing for the exercise of expert judgement.

Accumulating site or location specific results

7. The following guidelines should be used to derive the overall assessment score for an option from separate assessments of impact on a number of separate key environmental resources:

• Most adverse category. The principle here is that an option as a whole should be assessed according to the most adverse assessment of the resources affected. For example, if an option affects, say, five resources, of which one is in the 'large adverse' category and the remaining four are 'slight adverse', then the overall assessment score should be 'large adverse'. The rationale for this approach is that highly adverse impacts should not be diluted or masked by less adverse impacts. It also encourages the development of alternative options which avoid such adverse outcomes.

• Cumulative adverse effects. The principle here is that, where it is clear that there is a cumulative effect across a range of resources, then the option as a whole should be scored in a higher category than the resources in isolation. For example, a proposal may affect a number of resources, each of which is assessed 'slight adverse'. Where it is clear that there is a cumulative effect across the resources, the option as a whole would be assessed as 'moderate adverse'. The existence of cumulative effects will usually depend on there being some similarity in the characteristic features or attributes of the affected resources. For example, a group of biodiversity sites might all be habitats for the same species of plant or animal.

• Balancing adverse and beneficial effects. The principle here is that, where there is a genuine compensatory effect, adverse impacts on some resources may be balanced by beneficial impacts on others. The key issue is whether there are genuine compensatory effects. In most cases, it will be necessary to consider the impacts on each resource at a detailed level, to ensure that the features lost from one resources are provided at another. For example, adverse impacts on groundwater supply at one location would probably need to be offset by beneficial impacts on groundwater supply at another location beneficial impacts on floodplain would probably not provide genuine compensation. The scope for genuine compensatory effects will often be determined by the substitutability of attributes. In most cases, there is great uncertainty about the scope for substitutability, thus balancing should err on the side of caution. In particular, balancing should be restricted to 'slight' or, exceptionally, 'moderate' impacts. It is very unlikely that adequate compensatory effects can be identified to justify any balancing of 'large adverse' or 'very large adverse' impacts.

8. Clearly, these guidelines require an understanding of the key environmental resources and the impacts of the option on them. In addition, judgement and expertise are required to apply them satisfactorily.

Reporting

9. Good reporting is a key factor in ensuring that assessments are transparent and acceptable to steering groups and stakeholders. Reporting should include the following:

• the assessment of impact for each key environmental resource should be clearly summarised, distinguishing between the characteristics of the resource and the nature of the impact on the resource

• a summary list of resources and their specific assessments should be provided

• a statement should be provided, explaining how the overall assessment has been derived from the resource specific assessments and giving particular emphasis to the reasons for any cumulative adverse and balancing effects adopted

• in addition to the overall assessment and a qualitative comment, the Appraisal Summary Table should provide (in the quantative column) a summary of the numbers of key environmental resources in each scoring category

Updated: July 2003