The detection of asbestos in soil is becoming a pivotal point in the redevelopment of brownfield sites and the contaminated land projects.
However, for many developers and demolition and construction companies, the risks associated with asbestos in soil can sometimes be overlooked or underestimated at the desk top stage.
Consequently asbestos is commonly identified during subsequent ground works or only after demolition or redevelopment works begin.
Asbestos can find its way into made ground and soils in many different circumstances. These include the historic demolition of buildings containing asbestos containing materials (ACMs), fly-tipped waste, earlier use of the site and previously ineffective remediation of areas that may have been suspected as being contaminated.
Very low concentrations of asbestos fibres may therefore be present in soil and made ground and these fibres may not be visible to the naked eye.
The control limits stipulate that if the work generates less than 0.6 fibres/cm³ over 10 minutes or less than 0.1 fibres/cm² over four hours, then it is non-licensed work. If these levels are exceeded, then the work becomes licensed (and the contractor must be a HSE Asbestos Licence holder). In all situations the work must be carried out by suitably trained personnel and companies.
For those involved in the contaminated land sector there are many legal and regulatory obligations that need to be considered in relation to the potential asbestos contamination of soils and made ground.
To meet all regulatory requirements, and to ensure that the potential presence of asbestos in soils is assessed in the required manner, soil samples are assessed in a tiered process to identify if asbestos is present (qualitative analysis), in what composition (asbestos type determination) and in what quantity (quantitative analysis).
Prior to undertaking a site investigation, an initial ‘site pick’ of ACMs at the surface may reduce the likelihood of asbestos fibres being disturbed. However, in order for a sampling strategy to adequately characterise a site for ACMs, soil samples sent for laboratory analysis should be targeted both horizontally and vertically, importantly including visual assessment of excavated soil arisings.
Trial pit and borehole sampling are carried out through the made ground layer on a site or land area and 1 kg (approx. 1 litre) of soil is sampled. Careful attention is applied throughout the sample collection and handling in the laboratory to avoid any spread of potential contamination. Trial pits and borehole locations in the site under review are properly reinstated.
This original soil sample is screened for visible asbestos products, in the laboratory, which if present are weighed and analysed. Further analysis for asbestos fibres is undertaken and these are also separated and weighed. Measured weights are then scaled back up to represent the whole sample and an overall percentage asbestos content is determined.
On those occasions where asbestos products or fibres are not detected, and subject to a client’s request, further sedimentation analysis can be carried out. This involves a sample of soil being dissolved in water and an aliquot is then passed through a filter. The filter is then then analysed using SEM and EDS.
To minimise risk it is vital that all those with a responsibility for the management of asbestos, or who could potentially come into contact with it during building works, should have the right knowledge, training and support to deal with it safely.