What are asbestos fibre concentration limits in soil?

If you are responsible for land in the UK, perhaps as a landowner, developer, consultant, or contractor, you will need to know something about asbestos fibre concentration limits in soil.

After all, any disturbance to such land could potentially release asbestos fibres into the air, which someone nearby could then breathe in. The inhalation of this now-banned substance is linked to an elevated risk of developing certain potentially fatal diseases, such as mesothelioma or asbestos-related lung cancer, in later life.

However, the safety angle isn’t the “only” one that you will need to concern yourself with when it comes to asbestos-contaminated land. That’s because the discovery of asbestos in soil can also quickly turn what may have been a straightforward project, into a regulatory and financial headache.

The rules that determine whether your soil is “safe to leave”, “reusable on site”, or “hazardous waste to be disposed of”, isn’t based on the simple percentage of asbestos that you might see on a bulk sample certificate. Instead, it is a very different metric – asbestos fibre concentration – that you will need to educate yourself about.

In this article, we will explain such topics as what the current UK limits are, how they are measured, and most importantly, what they mean for real-world decisions on planning, excavation, disposal, and long-term land management.

What do we mean by “asbestos fibre concentration” when talking about soil?

To ensure the accurate assessment and management of asbestos in soil, it is vital to understand certain terminology, and the distinctions between the commonly used terms.

• “Asbestos-containing materials” (ACMs) or “fragments” refers to visible pieces of debris that a competent person can identify with the naked eye. Examples of such pieces include the likes of asbestos cement sheeting and insulation board.
• “Free fibres” are microscopic, individual fibres dispersed within the soil matrix. These fibres are often only identifiable in a laboratory.
• “Percentage asbestos content” (% w/w) is the concentration by weight, with w/w meaning “weight by weight”. This figure is used to determine weight classification, and it also influences risk assessments.

Regulators such as the Environment Agency, the Health and Safety Executive (HSE), and local authorities are primarily concerned with free fibres. This is because these are the fibres liable to become airborne during disruptive activities like digging, screening, or vehicle movements.

The legal trigger levels are therefore expressed as mass of free asbestos fibres per mass of soil (usually % or mg/kg), rather than as a simple percentage of visible asbestos debris.

How are asbestos fibre concentration limits in soil defined in current guidance?

There is no official UK limit for asbestos concentration in soil. However, asbestos fibre concentration limits in soil are principally defined in national guidance by two key thresholds based on weight percentage: 0.1% w/w for waste classification, and 0.001% w/w as a trigger for the Control of Asbestos Regulations 2012 (CAR 2012) and risk assessment.

These limits should not be considered to represent “safe” values. Instead, it is important to regard them as action levels that determine regulatory requirements and necessary control measures:

• Hazardous waste threshold (greater than or equal to 0.1% w/w) – Soil is classified as hazardous waste if it contains free and dispersed asbestos fibres or identifiable ACM fragments at or exceeding 0.1% by weight.In the event of any visible asbestos debris being present in the soil, it will be automatically classified as hazardous, irrespective of the percentage by weight analysis. This classification is crucial for disposal procedures, which involve specific waste transfer documentation and disposal at a licensed facility.

• The Control of Asbestos Regulations 2012 threshold (greater than or equal to 0.001% w/w) – CAR 2012 is the overarching legislation for the management of asbestos in Great Britain. These regulations apply to work involving soil that contains at least 0.001% w/w of asbestos. Work at this level is generally considered to be non-licensable. Nonetheless, a formal risk assessment is still required, along with an asbestos management plan (AMP), appropriate control measures (such as personal protective equipment and damping down), and specific training.

• Negligible risk (less than 0.001 w/w) – CAR 2012 does not typically apply in instances where the asbestos concentration is below 0.001%. However, there may still be a need for professional judgement and a site-specific risk assessment, particularly for sensitive end-uses such as residential developments.

How are asbestos fibre concentrations measured during soil investigations?

A tiered approach is used to measure asbestos fibre concentrations in soil. Visual inspection is combined with accredited laboratory techniques, primarily polarised light microscopy (PLM), and quantitative methods like gravimetric analysis and fibre counting.

Specialist laboratory methods are required for the measurement of asbestos in soil, due to the uneven distribution of contamination.

• Sampling: sampling strategies need to account for variability. Composite sampling techniques are frequently used, followed by analysis to determine the average asbestos concentration and distribution.
• Laboratory methods: initial examination is typically done under low magnification (microscopy), followed by the use of PLM or phase contrast microscopy (PCM) to confirm asbestos type. Methods like sedimentation and fibre counting are used for the precise quantification of free fibres, which have a typical Limit of Detection (LoD) of 0.001% w/w.

Quantitative analysis is crucial for waste classification and risk assessment, given that visual screening alone is not sufficient to identify microscopic free fibres.

How do fibre concentration limits influence the classification of soil as hazardous or non-hazardous waste?

Fibre concentration limits directly determine disposal routes and the strategies that will need to be used for remediation.

• Waste classification: if the 0.1 w/w threshold is exceeded, or if visible ACMs are present, hazardous waste disposal will be necessary. This is the most expensive option.
• Remediation: in the event of lower concentrations (below 0.1% w/w) being found, more flexible and cost-effective on-site management options – such as segregation, capping/cover systems, or reuse – will be possible under a materials management plan (MMP).

Higher concentrations trigger stricter control measures. There may be a need, then, for specialist licensed contractors, as well as for enclosed work areas, and enhanced air monitoring to protect workers and the public.

How should land managers interpret fibre limits alongside other risk factors?

It is essential for concentration data to be interpreted in context with other site-specific factors, such as:

• Soil concentration: the ease with which fibres become airborne will be impacted by such factors as moisture content (given that damp soil suppresses fibre release), particle size, and soil type (for example, clay vs sandy).
• Land use: a low concentration of asbestos may be acceptable for a car park where the scope for disturbance is typically low. However, it could present an unacceptable level of risk for a children’s play area, a residential garden, or another future use where the soil would be easily disturbed.
• Exposure pathways: such other critical factors as the potential for human contact, the proposed development plan, and proximity to receptors (for example, neighbours and workers) will also need to be considered.

What documentation and evidence should dutyholders keep when dealing with soils near or above asbestos fibre limits?

Regulators will expect dutyholders to maintain comprehensive records. This will be essential for the purposes of compliance and protecting against future liability claims.

Examples of key documentation include:

• Site investigation reports, encompassing detailed findings of asbestos presence, type(s), and distribution.
• Laboratory data, with results from UKAS-accredited laboratories confirming fibre concentrations and methods used.
• Risk assessments setting out potential exposure pathways and proposed control measures.
• An in-depth materials management plan (MMP) when soil is to be reused on-site. Such a plan will be crucial for justifying the reuse strategy and demonstrating compliance.
• Waste transfer/consignment notes, which are essential documentation for all off-site disposal, including correct European Waste Catalogue (EWC) coding.
• Validation reports, which are issued after remediation to confirm that the work was completed as planned and the site is safe for its intended use.

Conclusion: what should dutyholders take away from today’s asbestos fibre concentration limits?

Asbestos fibre concentration limits are foundational thresholds in UK land management that guide safe decision-making. So, it is of the utmost importance for dutyholders to understand these fibre limits, in addition to ensuring accurate measurements and proper interpretation.

When land managers adhere to such practices in line with the latest applicable guidance, they will go a long way to protecting workers, neighbours, and future users of the land.

Good practice entails proactive assessment during the early planning stages. This, in turn, will help avoid costly disposal errors and ensure compliance throughout a project’s lifecycle.

To learn more about how our own expertise at Oracle Solutions can support your efforts to responsibly manage soil with asbestos content, please enquire to our team today.