Effective Coal Mining Risk Assessment for Safe Development

Determining if Your Site Lies in a Development High Risk Area​​​​

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The Mining Remediation Authority (MRA, formerly the Coal Authority) refers to areas with likely risks from past mine workings as Development High Risk Areas, and determining whether a site is located in such an areas is the essential first step of a risk assessment. It is is then necessary for a CMRA to determine, as accurately as possible, the location and depth of known mine workings and entries in relation to the site, based on available records. If the land falls within a Development High Risk Area, the local planning authority (in consultation with the MRA) will usually require a CMRA to accompany your planning application.

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The Mining Remediation Authority has an interactive map viewer that allows developers and consultants to check whether their site is within an area potentially affected by past coal mining. However, confirmation should always be sought through the local planning authority as to whether a CMRA is needed and provide details on planning and permitting requirements.

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When a CMRA May Not be Required

The scope of a Coal Mining Risk Assessment should be appropriate to the proposed development and the associated risks. Developments that involve minimal ground disturbance, such as the installation of storage containers, small structures or solar panels, would be considered low risk and may not require an assessment. Similarly, changes of land use that do not include excavation or construction work might not require assessment.

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That said, local authorities have discretion to request further information if they believe potential risks exist. Early engagement with the planning authority therefore remains the best approach to confirm exemptions and avoid unnecessary delays. If your plans involve excavating near coal seams or former mine workings, then and a risk assessment and an MRA permit are likely to be required before starting work.

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It should be noted that mining and extraction risks can exist in areas outside the those affected by coal mining, as other minerals and resources such as salt, chalk and metal ores (lead, tin, iron) have been historically extracted from areas across the country and can present risks similar to those associated with coal mining. Assessment of non-coal mining risks is therefore an important consideration for sites outside coal mining Development High Risk Areas.

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Understanding the Coal Mining Risk Assessment Process

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A CMRA determines the likelihood of coal mining mining features being located on or beneath the site, and the potential impact of these features on a proposed development. It is typically prepared by a qualified geologist or geotechnical engineer with experience in ground investigation and mining processes. Understanding the nature of previous extraction activities and their potential influence on site conditions is the foundation of an accurate assessment.

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The assessment begins with a desk-based review, analysing geological maps, historical mine plans, and data from the Mining Remediation Authority. The purpose is to identify whether the site could be affected by surface or underground mine workings, mine entries or other legacy features. The findings will generally inform the scope of subsequent investigations to confirm the presence and extent of mining-related features and determine the scale of any risks.

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Key Components of an Effective CMRA

A well-prepared CMRA provides a detailed overview of the site, including its location, development proposals and coal mining context. It assesses the potential for instability, subsidence, gas emissions and surface collapses resulting from historic mining. Where research reveals the presence of features such as mine entries, their positions and depths are noted based on the information contained in the available records. Available records may include co-ordinates, depths, dimensions and details of any past remedial or capping works.

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The report will usually include a strategy to physically investigate the identified features and details of how coal mining features may influence the site layout and design. For example, buildings cannot usually be located within the influence zone of a mineshaft (the zone of potential collapse), even after the shaft has been treated and capped.

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The primary information source for a CMRA are the records held by the MRA, which may include mine plans, shaft locations and dimensions, coal seam thicknesses, records of subsidence and mine gas emissions, and details of any previous treatment. This can be supplemented by geological maps and records and the findings of any site investigation that may have been undertaken on the site. The available information is interpretated to determine the risks associated with past mining and the most appropriate course of action to investigate and mitigate the risks.

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Assessing and Managing Site-Specific Risks

Each site within a coalfield will have specific risks depending on its mining history and geological characteristics. Available records may reveal underground workings or coal seams at shallow depth (generally considered to be within 30m of the surface) that could compromise ground stability. Intrusive investigations are commonly required to verify the presence of features such as voids, loose ground or intact coal seams, that are indicative of former mine workings and may require remedial measures to reduce the risks of ground instability.

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Treatment of mine workings and shafts usually involves grout stabilisation, which is designed to prevent the potential for collapse. In some cases, the design and layout of a development can be amended to mitigate risks. For example, ‘no-build’ zones may be appropriate over or near mine entries, or where larger industrial buildings are proposed over known mineshafts, structural reinforcement or ground improvement may be sufficient to mitigate the risks where a no build zone would impact development viability.

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The CMRA is the initial step to determining the most appropriate solutions and helping developers avoid costly complications during construction and ensure regulatory compliance.

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Surface Stability and Underground Impacts

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The basic aim of a CMRA is to identify features that can cause instability at the surface, that may present as subsidence, voids, sinkhole-like features and ground collapse, and which present a risk to structures. Mine workings beyond a certain depth (a general rule of thumb is a depth greater than 10 times the thickness of the worked seam) will not usually be considered to present of risk of instability at the surface.

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Where underground mining has taken place at shallow depths within the influencing distance of the surface, mine workings will most likely require treatment before a development can proceed. Where any unrecorded coal seams, workings or collapses are encountered during excavation or investigation works, these must be reported immediately to the Coal Authority and will also likely require treatment.

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Developing Effective Mitigation Strategies

Once risks have been identified by the CMRA, an investigation and treatment plan is required, which will detail the scope (extent, depth) of investigation works and the mitigation strategy required to address the risks. The investigation and treatment of mine workings is undertaken by specialist contractors who have the necessary resources (personnel, specialist equipment) and experience required to ensure the remediation works, most commonly in the form of grout stabilisation, are carried out to the required standard.

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The strategy should detail how treatment will address the coal mining legacy in the context of the development proposals, and the how the development will be adapted (as necessary) where risks remain after treatment. This may include adapting foundation designs, undertaking ground improvement works or incorporating gas management systems should a risk from mine gases be identified.

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Working with Local Planning Authorities