Environ's Claire Holman outlines new guidance from the Institute of Air Quality Management (IAQM) to aid impacts assessments in construction
In December 2011, the IAQM published new guidance to assist in the assessment of air quality during the construction of new developments. The publication, entitled Guidance on the assessment of the Impacts of Construction on Air Quality and the Determination of their Significance, was published following a review of 10 leading consultancies’ assessment methods which uncovered widely differing approaches.
Researchers have found evidence that major construction sites increase the number of days when concentrations of airborne particles known as PM10 exceed the national air quality objective value, as well as increasing long-term average concentrations.
With epidemiological research showing there is no threshold below which there is a safe concentration of PM10, these increases are likely to be associated with adverse effects on human health, further emphasising the importance of getting assessments right. Construction dust can also cause a loss of amenity and complaints due to the soiling of surfaces.
Both PM10 and dust emissions can occur during the preparation of the land (demolition and earthworks, for example) and construction. The impacts can vary substantially from day to day depending on the level of activity, the specific operations being undertaken, the weather conditions and the mitigation measures being applied.
A large proportion of the emissions results from vehicles moving over temporary roads and open ground. If mud is allowed to get onto public highways, dust emissions can occur at some distance from the originating site, a phenomena known as track-out.
The scientific evidence on the distance over which impacts may occur is limited. Extensive monitoring of PM10 concentrations around construction sites has occurred since best practice guidance was first published by the Greater London Authority (GLA) in 2006, however, the data is collected on a site-by-site basis, by developers who have no direct interest in funding an analysis of the data and publishing the findings.
Probably the best evidence available is in an unpublished BRE study for the GLA commissioned to inform the development of its guidance. It suggested that the impacts on PM10 concentrations from a major construction site with good mitigation occur over a distance of less than 150metres, but due to the locations of its monitoring sites, more precise information is not available.
The IAQM review of consultants’ approach to air-quality assessments found that:
- the distances used varied from 100m to 250m from the site boundary, depending on whether mitigation was assumed or not;
- few considered the effects of construction on PM10 concentrations despite the known health effects or the impacts of mud tracking-out from sites;
- several referred to the GLA guidance when assessing sites outside the capital, despite the fact that it doesn’t provide an assessment methodology; and
- other consultants referred to the example of dust sensitive receptors in Mineral Planning Statement 2, but this is based on work more than 20-years-old and it is not universally accepted. For example, it considers residential areas as medium sensitivity to dust emissions, whereas many air quality practitioners would consider them to be highly sensitive.
As a result of these findings, an IAQM working group spent a year developing new guidance on assessing air-quality impacts from construction sites, working closely with the GLA, which is currently revising its best practice guidance.
The new IAQM guidance is aimed at proving developers, their consultants and environmental health officers with a consistent framework for carrying out air-quality impact assessments.
The effects of a construction site on air quality depend to a large extent on the mitigation measures adopted, and therefore the guidance emphasises the need to identify the risk of effects, in order to then identify the appropriate mitigation.
The guidance defines the development site or, if it is a large site, the development phase, as negligible, low, medium or high-risk, based on the potential for PM10 and dust to be released and the distance to the nearest receptor.
For the assessment and associated mitigation, the guidance divides activities that may take place on a construction site into four general dust generating activities:
- demolition;
- earthworks;
- construction; and
- track-out.
Once mitigation has been specified the guidance requires the overall risk of effects and their significance to be identified based on the sensitivity of the surrounding area. For example, a site surrounded by high-rise housing in a city centre is likely to be far more sensitive to the air-quality impacts of a construction site than a suburban site with a few houses several hundred meters away.
Lastly, the guidance does not just take account of the potential effects on people, it also considers the direct effects of dust deposition on sensitive ecological receptors.
The guidance (available for download from the IAQM website) is primarily for use in the UK, however it may be applied elsewhere as long as careful consideration is given to its applicability in different climates and where working practices on construction sites may differ significantly.
This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.
Dr Claire Holman is a principal consultant at ENVIRON and a commissioner for the Commission for a Sustainable London 2012. For further information or to feedback on the guidance contact Dr Holman at [email protected]
