This article has been superseded by Safety Guidance – Classification of Potentially Contaminated Sites for Intrusive Investigation Activities which was published in March 2024.

It’s a red site. So what?

It was the 15th century Swiss medical pioneer Paracelsus, who noted in his journals: “all substances are poisons; there is none which is not a poison. The right dose differentiates a poison.” Although he made this statement almost 500 years ago, it is now known and proven to be correct with substances known to be essential for human existence, such as salt, defined as toxic when administered in sufficient quantities. For this reason the classification used by the British Drilling Association (BDA) Guidance for Safe Intrusive Activities on Contaminated or Potentially Contaminated Land and part four of the Site Investigation Steering Group (SISG), where sites are classified into green, amber or red sites, must be fully understood and not applied casually. Failure to fully appreciate the relationship between quantity and substance classification could be as dangerous as doing nothing or impose expensive non essential protection measures.

The BDA guidance classifies red sites as the most hazardous, attributing this classification to sites where there are: ‘Substances that could subject persons to risk of death, injury or impairment of health. Examples would be any substances that are corrosive, acidic, carcinogenic, cause skin irritation or respiratory problems, affect the nervous system, affect the organs, etc.’ Unfortunately this classification takes no account of the quantities present which are critical to determining the risk category as even uncontaminated soils and dusts, if present in the correct quantities and form, could act as a skin irritant or be harmful to the respiratory system. It would be a rare site investigation which did not include these hazards and on this basis, all sites would be classed as red.

In the BDA guidance, reference is made to the need for a risk assessment and this is the key to correctly determining the nature and category of the site. The green, amber, red categorisation system provides a simple warning and flagging system but where the presence of hazards is known or suspected, an assessment of both the nature and the quantity of the substances is required and this poses a problem for conducting work on contaminated land. In the majority of cases the purpose of conducting a site investigation is to determine the presence and quantity of contaminants for human health risk assessments. Until such time as this is done it is impossible to produce a definitive risk assessment and as such some assumptions need to be made.

To make an assessment there needs to be an understanding of the site and surrounding areas. A desk study should be able to identify the history of the site, in particular the industrial uses to which it has been put. This is the first stage but by no means the end of the process as not all uses may have been logged or recorded and they may not reflect the current use. Nothing substitutes a visit to site to examine the visible evidence but commercially, particularly on small sites, this is not always possible so any evidence such as photographs, discussions with clients etc. will help to build the picture.

Once the history and past uses of the site has been identified, an indication of the potential contaminants can be gathered but the available sources of guidance do little to clarify the situation. There are a number of publications used commonly to determine the presence of substances for the purposes of human health risk assessment, with the Environment Agency publication CLR8 – ‘Potential Contaminants for the Assessment of Land’ being recognised as the closest thing to definitive but the purpose for which it was developed does not fully suit our needs in term of occupational safety and health.

CLR8 is intended as an aid to determining the substances to be tested in a contamination study for human health but is not specific enough to assist completely in determining the requirements for the successful management of exposure in the course of site work or activities. CLR8 suggests everything is present in some quantity on nearly all sites but provides little indication of possible concentrations, the form of the substance or the exact location on the site. As an example, CLR8 identifies the presence of ‘oil / fuel hydrocarbons’ at airports, which although suggestive of contaminants which will certainly exist at some points on the site provides little guidance for occupational safety risk assessment. Hydrocarbons used for fuel vary from heavy oils such as diesel and more volatile substances such as pentane and if the whole site is treated as containing such substances, all area would be classified as ‘red’ under the BDA guidance as it is likely these hydrocarbons could contain benzene (a carcinogen), pentane (produces narcosis in higher volumes) and possible lead (causes damage to the peripheral nervous system).

A study undertaken by the author of this article, cross referenced all the potential contaminants present on sites as indicated by CLR8 with the risk phrases attributed to the compounds, suggested every site identified should be rated as the highest possible risk, if the categorisation of sites is dependant on the presence of substances alone, as suggested by the BDA guidance, all geotechnical sites would be classed as ‘red’ which is clearly unfeasible.