EIA - assessing in-combination effects

31st August 2016


Related Topics

Related tags

  • Generation ,
  • Fossil fuels ,
  • Business & Industry ,
  • Built environment

Author

Miriam Billig

Pete Collins, senior environmental consultant at Atkins, describes how in-combination effects were identified on a large gas power plant.

There is no accepted method for assessing in-combination effects of a development, where the same receptor is affected by the same scheme in different ways, such as a resident experiencing both noise and air pollution. It is different from cumulative effects, which is the effect of similar impacts from multiple schemes on the same receptor.

It is difficult even to conceptualise in-combination effects in a quantitative or standardised manner, for example, how can you add decibels to parts per million in a meaningful way? The only way to assess the likely in-combination effects on a receptor is to consider each receptor and the effects on it in turn, informed by the experience of an EIA practitioner. This can be a daunting prospect given the number of receptors that may be considered in an environmental statement (ES).

This article describes a framework used for a recent project for considering in-combination effects, and a filtering method for significantly reducing the number of receptors that need to be considered.

The proposed development is a 299 MW gas-fired power station on the site of the former Meaford A and B coal fired power station on a business park in Staffordshire. The site is in a predominantly rural area, with local homes nearby and the Trent and Mersey Canal adjacent to its eastern boundary Construction is expected to take three years, with a life span of 35 years. Permission for the energy centre is through the Development Consent Order process, since it is nationally significant infrastructure.

In order to determine which types of effects a given receptor may be subject to, the first step is to group the receptors into categories. For the energy centre, we identified the following categories:

  • Humans, property, ecology, historic environment, landscape, controlled waters, the economy, and local waste infrastructure.

The next step is to identify all the assessed topics that might affect a particular category. This is analogous to developing a source-pathway-receptor model as frequently done for contaminated land assessments. The drawing below shows ‘sources’ in red, ‘pathways’ in green, and ‘receptors’ in blue.

Note that some topics can be more than one of these, for example water can be considered both as a receptor (a controlled water body in its own right), and as a pathway (such as where aquifers are used for drinking water). The arrows show all the different ways that human receptors might be affected. This exercise should be repeated separately for all receptor groups identified. This exercise allows us to identify the ES chapters relevant to each receptor group. For humans, as shown in the figure, the relevant chapters are:

  • Socioeconomics, traffic, air quality, noise, visual, ground conditions, and water.

Source-pathway-receptor model for humans

The filtering process can now begin:

  • In each chapter, we identify every specific receptor (in the case of humans, specific residential addresses, staff or users of specific facilities) and then determine which are affected by more than one topic. For example, noise and air quality will usually affect a similar set of specific receptors.
  • We disregard specific receptors for which all effects across chapters are identified as ‘none’, ‘neutral’, ‘negligible’, or equivalent terminology. We also disregard any receptors that cannot be confidently identified across chapters, such as a generalised ‘local employees’. We can also disregard ‘double counting’, for example, the water chapter may consider ecological receptors but if the ecology chapter has already taken this potential pathway into account we need not consider it again.

In the case of the energy centre, this process left only a handful of receptors that were expected to be affected in any notable way. This reduced volume allowed us to consider each receptor on a case-by-case basis for in-combination effects. In this project, the only in-combination effect identified was on recreational users of the Trent and Mersey Canal who, during construction, may be affected by both moderate adverse visual and major (brief) adverse noise effects.

In summary, the assessment of in-combination effects requires each receptor to be assessed individually by an experienced EIA practitioner. The only practical way of doing this is to filter out all the receptors where no such in-combination effect is possible, thereby reducing greatly the number of receptors that need to be considered.

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