What does long-term monitoring of asbestos remediated soil involve?

Even after the thorough removal of asbestos-contaminated soil is complete, this will rarely be the final step when it comes to long-term safety and regulatory compliance.

For dutyholders, developers, contractors, and land managers, it is essential to understand the necessity and mechanics of ongoing surveillance.

The long-term monitoring of a given site post-remediation provides vital assurance that public health and environmental safety are being maintained. It is key to protecting future works, land use flexibility, and regulatory compliance.

In this article, we will set out the structured and risk-based approach necessary for designing and executing a long-term monitoring programme for sites where asbestos has been managed in the ground.

What triggers the need for long-term monitoring after asbestos remediation?

It can be easy to presume that the term “asbestos remediation” must always refer to operations where every trace of asbestos is removed from a given site. However, this is not always the decision that is made. Instead, engineering solutions may be adopted for particular land that involve the asbestos contamination being managed in situ (in place).

The need for long-term monitoring of a site is primarily driven by the remediation strategy itself, as well as the planned future use of the land.

Typical scenarios necessitating a formal, long-term monitoring plan include:

• Partial removal, where some residual asbestos remains below a certain threshold or in inaccessible areas
• Encapsulation or burial cells, which are sites where significant quantities of contaminated soil are consolidated and buried on-site under a barrier
• Capping/cover systems, which entail the installation of clean soil layers or hard standings (such as concrete or asphalt) over contaminated ground
• Areas of phased development, where it is anticipated that development will occur incrementally over a number of years.

The remediation method will directly influence the monitoring approach that is required. For example, a concrete hardstanding won’t typically require the same frequency of intrusive monitoring as a clean soil cap in a landscaped area.

Regulatory expectations can also differ significantly, depending on the specific type of site involved. An industrial site, for instance, might tolerate a higher level of engineered control reliance. On the other hand, a future agricultural or residential site will demand stricter verification that no fibres can reach the surface, where exposure pathways may be likelier.  

How is a long-term monitoring plan designed for remediated asbestos-contaminated land?

For a long-term monitoring plan to be effective, it will need to be site-specific and risk-based.

A good plan will typically encompass such elements as:  

• An updated Conceptual Site Model (CSM) showing where asbestos remains, as well as potential pathways (how fibres could move) and possible receptors (such as people, animals, and the environment).
• Risk-based decisions, with the frequency, depth, and location(s) of checks determined by the likelihood of asbestos exposure. There will be a need for higher-risk areas, such as erosion-prone slopes or areas of planned excavation, to be monitored more intensely.
• The integration of other ongoing site controls, such as land-use restrictions, the clear demarcation of managed areas, and permit-to-dig systems for intrusive ground works.
• Defined action levels, with the plan specifying clear thresholds that, if exceeded, will trigger specific interventions or further investigation.

What soil sampling and inspection methods are used during long-term monitoring?

The long-term monitoring of asbestos remediated soil depends on a combination of visual and analytical methods to verify the integrity of the engineered controls:

• Visual inspections take the form of regular, scheduled walkovers to check the surface condition of capping layers. The focus is on looking for signs of erosion, subsidence, vegetation stress, or evidence of unauthorised digging or disturbance. This process is typically documented heavily with photographs and checklists.
• Intrusive soil sampling is also undertaken on a scheduled basis, to confirm that buried asbestos is not migrating vertically or laterally. This is carried out at predefined depths and locations, with samples then undergoing analysis using UKAS-accredited laboratory methods.
• Air monitoring is generally only used during active ground disturbance, such as planned maintenance or construction, or if visual inspections find that a significant breach of controls may have occurred. It isn’t very common for routine ambient air monitoring to be conducted at a sealed site, unless a specific risk pathway has been identified.

Recurring results are rigorously compared against the initial remediation validation data, as a means of tracking stability at the site over time.

How are asbestos fibre concentrations assessed over time?

The laboratory analysis of soil samples typically involves techniques such as gravimetric analysis and microscopic counting (for example, using polarised light microscopy, or PLM).

This is in accordance with UK guidance such as the Health and Safety Executive (HSE)’s Asbestos: The Analysts’ Guide document (under the series code HSG248).

• Trend analysis is carried out, whereby consultants look for patterns that might indicate a barrier’s deterioration. If fibres suddenly appear in a clean surface layer where none were previously detected, this will be a clear trigger for investigation.
• Thresholds and action levels also play an instrumental role. While generic regulatory limits do exist, site-specific action levels are often used. In the event of these levels being exceeded, there will be a need for immediate action. The response could be to repair a cap, for instance, or the entire site management plan may be re-evaluated.

What signs indicate that a remediation barrier or engineered control is failing?

By identifying indicators of failure at the earliest possible stage, dutyholders can put themselves in a position to intervene sooner, thereby preventing an emerging issue from escalating.

Some key signs of failure are detailed below.

• Soil sample indicators: if analytical results show an unanticipated increase in fibre concentration in layers that were previously validated as clean, this is a classic indicator that failure is taking place.
• Surface indicators: these encompass such “symptoms” as cracks emerging in hardstanding, a soil cap having undergone significant erosion, and/or indications of deep burying animal activity. Dead vegetation may also be a telltale sign, as underlying material changes might be to blame for this.
• Migration routes: you might see evidence of mechanical disturbance from vehicles or site users, or of water pooling or washing away surface material.

If any of these signs become apparent at an asbestos remediated site, consultants will need to undertake immediate resampling and inspection, to verify whether an apparent issue is genuine or an incidental, isolated incident.

How are monitoring results recorded, reported, and communicated to stakeholders?

A high standard of recordkeeping is crucial. The dutyholder will need to maintain a comprehensive and easily accessible repository of all monitoring results, site plans, permit-to-dig records, and inspection reports.

It is of critical importance for monitoring outcomes to feed directly into ongoing site management plans for asbestos remediated land. Transparent information-sharing will be necessary across all stakeholders, including contractors, new owners, tenants, and regulators, to ensure everyone is aware of restrictions and risks.

Such proactive and clear reporting and communication will help prevent costly remediation or project delays during future activities at the given site.

When and how is long-term monitoring adjusted or scaled back?

The long-term monitoring plan is a necessarily dynamic plan, adjustable based on performance.

• Reducing frequency: if several years of data from the site consistently show stability and compliance, the decision might reasonably be taken to scale back monitoring frequency (for example, from annual to biannual inspections).
• Intensifying monitoring: there are certain circumstances in which it will be necessary for monitoring to be stepped up. These include during phases of redevelopment, a planned change of land use, or immediately following damage to a capping layer.

The goal will be to eventually satisfy regulators that the site is safe for its intended use, thereby possibly allowing for intensive monitoring to be brought to an end. However, perpetual duties to manage the land securely will remain.

Conclusion: what should land managers expect from a well-run long-term monitoring programme?

Effective monitoring of asbestos remediated land over an extended period of time is of the utmost importance for ensuring safety and compliance. It replaces uncertainty with verifiable data, which assures dutyholders that risks are controlled and engineered solutions continue to be effective.

For land managers, a reliable monitoring record is a crucial asset, providing transparency while guarding against future risks, costs, and disruption in relation to the asbestos remediated land.

Are you on the lookout for services and expertise that will help ensure the effective, safe, and compliant management of asbestos-contaminated land for which you are responsible? If so, please don’t hesitate to enquire directly to the Oracle Solutions team.