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Alternative site categorisation system for safe investigation of contaminated land

M J Baldwin of Norwest Holst Soil Engineering and W G Greenwood of ECoS Environmental


Each year in the UK, thousands of ground investigations are undertaken on sites containing potentially contaminated or known contaminated land. These investigations are generally performed by site investigation contractors, but increasingly by other parties with little or no knowledge of the site or appropriate ground investigation techniques.

During a recent seminar held by the British Drilling Association (BDA) and the Association of Geotechnical Specialists (AGS), it became apparent that the majority of companies undertaking ground investigations were ill-informed about the potential types and levels of contamination that could be expected on site. It was also evident, from speakers, that this lack of awareness stemmed from either ignorance or misuse of Volume 4 of the Site Investigation in Construction series (known as SISG 4) by the procurers of ground investigation services.

While most of the guidance in SISG 4 is extremely useful, the categorisation system which designates sites green, yellow or red requires updating. This paper proposes a new site categorisation system related to the health and safety of site operatives, which is based on the schedules contained in Section 143 of the Environmental Protection Act (1990).

Existing site categorisation system

SISG 4 was first published in 1993 following and making use of work carried out by the BDA in its guidelines. The aim of SISG 4 is summarised in the document's executive summary as 'to promote the use of safe working practices in the investigation of landfills and contaminated land.

They are intended for use by individuals or organisations who are involved in the planning, specification, procurement, supervision and execution of site work'.

Although it covers project requirements, contractual requirements, hazard assessment, health & safety and field operations, for many users the entire document is distilled into the site categorisation system presented in the appendix to Volume 4 which is reproduced in part in Table 1.

Use and misuse of the existing site categorisation system

In the authors' experience Volume 4 is very rarely used by procurers of site investigation services. This is borne out by the fact that only 5% to 10% of all enquiries regarding contaminated sites include any information with regard to a desk study and of these, only 20% have been assessed using Volume 4 guidelines.

Procurers say they do not make use of the system because they are ignorant of its existence, do not understand how to apply the guidance notes, or claim to lack the time. Although these reasons reflect the longheld view in the industry that procurers of site investigation services are not being 'educated' with the available guidelines, the authors are also aware of procurers' queries over the application of the existing site categorisation system.

There is growing evidence that both procurers and professionals involved with the implementation of site investigations believe the existing system to be too rigid, especially with regard to the yellow and red categories. If the procurer finds it difficult to decide whether a site should be classified as yellow or red, the tendency is to categorise it as red because this automatically transfers the risk to the organisation implementing the investigation. Similarly, greenfield sites are often classified as green on the assumption that no previous development has taken place. This potential misclassification of the site could and often does have cost implications and does nothing to help the reputation of the industry as a whole. Being able to make informed decisions on the likely levels of contamination on a site should ensure that site operatives are provided with the appropriate personal protective equipment (PPE) as shown above in Figure 1.

Basis for the proposed classification system

The proposed site classification in Figure 2 has been prepared specifically in relation to the health and safety of site operatives based on the following rationale.

Land becomes more or less contaminated by the use to which it is put.

The levels of concentration and toxicity of substances intentionally or, more likely, casually placed on the land during use, will lead to varying degrees of contamination. Due to the widespread and uncontrolled nature of historic land use, the actual amount of contaminated land in the UK is a matter for conjecture. The Government has estimated that as much as 65% (27,000ha) of derelict land should be regarded as contaminated while the remaining 35% may be contaminated. Therefore, with the increasing reuse of what are known as brownfield sites, most site investigations will be carried out on contaminated land.

To identify and define the problem, Section 143 of the Environmental Protection Act (1990) formally authorises the Secretary of State (at the moment under the control of the Department for the Environment, Transport and the Regions) to make regulations specifying contaminative uses of land and prescribing the form of registers and the particulars to be included in them. Local authorities would then have the responsibility of maintaining such registers and making them available to the public free of charge. Section 143 also defines a list of 16 possible contaminative uses ranging from dry cleaning operations to gasworks.

Although Section 143 has never been implemented in its original form (because of fears of a land blight), this use-based approach provides a succinct starting point for a site categorisation system although it has now been superseded by a risk-based approach in the Environment Act (1995).

It should be noted that the compilation of registers of contaminated sites, using a risk-based approach, is ongoing and not all sites have been classified. However, it would be prudent to contact the local authority to ascertain if the site has been identified as contaminated. In any case, the desk study information should identify what contaminative uses have been carried out on site in the past; ideally this should have already been done before any site work commences if the guidelines given in BS5930 have been followed.

If the site is not yet registered and a desk study cannot be carried out, it should be assumed the site is contaminated and precautions suitable to a red site be adopted as shown in Figure 2. In addition, the health & safety aspects of the site can then be reviewed as the work is being carried out and, if necessary, more suitable precautions taken.

Where a desk study has been undertaken the contaminative use can more easily be ascertained and the site classified using Section 143.

However it is worth noting that Section 143 does not, in its original form, offer a risk-based assessment of a site, and the site is solely classified according to its previous use or uses with no account taken of the extent of such a use or when it ceased.A recent case found that a garage, where the fuel tanks were removed some time ago, showed little hydrocarbon contamination due to the processes of natural attenuation. Therefore, in addition to the schedules given in Section 143, a basic risk assessment approach should be adopted. Simple questions such as those below would assist with site classification:

Are the general public allowed access to the site? Presumably, if the public have access, then the site or at least the near surface should be free of contamination.

Is the site obviously contaminated? It is astonishing the number of sites where site operatives, engineers and others have turned up only to find the site covered with asbestos, pools of unknown liquids on what has been classified as a 'green site'. A simple site visit, which should have been carried out during a desk study would alleviate this problem.

Is the site in use by the operator? If the site is still in use (and assuming hazardous processes occur on the site which would identify it as red) then under health and safety legislation, procedures must be in place for the site users. It could then be assumed that the site investigation team would not need to provide, to the same extent, the health and safety equipment required for a non-occupied red site.

Site safety equipment

The BDA guidelines suggest a three-tier system for site safety equipment based on the classification of green, yellow and red sites given in SISG 4. The categorisation scheme proposed here recommends an additional category of amber, in between yellow and red, such that the classification for inclusion as a yellow site is not as onerous as at present, while for red, it has become more onerous.

As a minimum for all sites, including green, a basic level of simple safety measures such as the provision and use of gloves and hard hats.

All sites should have washing facilities even if this means a static water supply, soap and towels. The most extensive protection is identified on red sites where full personal protection will be required (disposable overalls, waterproofs and boots, face masks) as well as fully functional decontamination units. Details of the personal protective equipment is given in Table 2 above.


It is hoped that this proposed categorisation system is more workable than the previous method and that site safety is no longer left to chance as it has been in the past. Nevertheless, site safety is not the sole responsibility of the site investigation contractor but also the consultant and client in providing all the necessary information (either as a desk study or site risk assessment) to enable the contractor to provide the necessary level of protection for their staff.


Guidelines for the Safe Investigation by Drilling of Landfills and Contaminated Land: Site Investigation in Construction, Volume 4. 1993.

British Drilling Association: Guidance Notes for the Safe Drilling of Landfills and Contaminated Land.1992

BS5930: Code of Practice for Site Investigations, British Standards Institute, 1999.

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