Mining legacy and the coalfield referral areas

If any part of your site sits in a Development High Risk Area, the council will expect a coal mining risk assessment planning document with the application, and it will consult the Coal Authority before deciding. Miss it and the application is either invalid or held until the assessment arrives. Neither is a good look on a programme that already has a land payment date in it.

The risk areas are published, they are free to check, and the check takes about two minutes. It is one of the few due diligence tasks on a development site that costs nothing and is routinely skipped.

How coalfield referral areas are defined

The Coal Authority holds the national records of coal mining, and it divides the coalfield into two categories for planning purposes.

Development High Risk Areas are the parts of the coalfield where recorded mining features could affect new development: mine entries and their zones of influence, recorded shallow workings, probable unrecorded shallow workings, mine gas outbreaks, recorded surface hazards and areas of past mine water problems. A minority of the coalfield falls into this category, but it includes a great deal of land in the Midlands, Yorkshire, the North East, Lancashire, the North Staffordshire area, Kent and South Wales.

Development Low Risk Areas cover the rest of the coalfield. Standing advice applies rather than a site specific assessment, and the Coal Authority is not routinely consulted.

The important point for scoping: the boundary is drawn from records, not from geology. A field with no visible mining history can sit inside a high risk area because a shaft was recorded 200 metres away, and a site with obvious spoil can sit outside it. Check the mapping rather than the appearance of the land.

Checking whether a site falls within one

Three checks, in this order.

1. The Coal Authority's published interactive mapping, which shows the development risk areas against an ordnance base. This tells you which category you are in and often flags the feature driving it.
2. A commercial coal mining report or the Authority's own report products for the site, which returns the recorded features rather than just the category.
3. The British Geological Survey records for the coal measures, faulting and any non coal mineral working.

Do all three at heads of terms stage. The difference between a low risk site and a site with a recorded shaft under the proposed block is a difference in build cost that belongs in the offer, not in a post exchange claim.

Where the site is in a high risk area, the Coal Authority becomes a consultee on relevant applications and the council will not usually determine the application without its comments. Building that consultation into the programme is easier than chasing it in week seven.

What a coal mining risk assessment contains

The assessment is a desk study with a conclusion. It is not a ground investigation, though it usually recommends one.

A usable report covers:

• The mining history of the site and the area, from the Authority's records, historic plans and abandonment plans.
• Mine entries within and adjacent to the site, with their recorded position, diameter, depth and treatment status, plus the accuracy tolerance of the record.
• Recorded shallow workings, their seam, depth and extent, and an assessment of the likelihood of unrecorded workings based on seam outcrop positions.
• Mine gas potential, including carbon dioxide and methane, and any recorded gas emissions.
• Surface features: spoil heaps, adits, drift entries, bell pits, sinkholes and any recorded subsidence.
• Mine water levels and any rebound issues.
• Conclusions on the risk to the proposed development, with specific recommendations: where intrusive investigation is needed, what form it should take and what design responses are likely.

The last section is what the case officer reads. A report that ends with a general statement that risks can be dealt with by condition is a report that will attract an objection. A report that says drilling is needed on a specified grid to prove or disprove workings at a stated depth, and that the design assumes grouting of any voids found, is one the Authority can support.

These reports should be prepared by someone with the relevant ground engineering experience. This is not a document to draft and hope, and a Geotechnical Assessment prepared alongside it will normally be expected by the council to carry a suitably qualified author.

Mine entries, shallow workings and standing advice

Mine entries are the most demanding feature to design around. A recorded shaft has a position accuracy that may be tens of metres, and a zone of influence around it within which the ground may collapse. Development is generally kept out of that zone, and the zone is usually treated as an area of open space, parking or landscaping rather than built form.

Two consequences for layout. First, the zone has to be located early, because moving a block after the layout is fixed is expensive. Second, proving the actual position of a shaft requires intrusive investigation, and the investigation itself has to be designed so that it does not destabilise the feature.

Shallow workings are handled differently. Where workings are recorded or probable at a depth that could affect foundations, the usual responses are drilling and grouting to fill voids, a raft or piled foundation designed for the ground conditions, or a combination. Where piling is proposed near existing buildings, the vibration and ground movement questions in our note on piling and vibration to neighbouring structures come into play alongside the mining risk.

In low risk areas, standing advice replaces the site specific assessment. Read it rather than assuming it says nothing: it typically still asks developers to consider mine gas where a basement is proposed and to report any unexpected features found during construction.

Permits for entering or disturbing coal

This is the part most often missed, because it is not a planning matter at all.

Unworked coal and coal mine workings in Great Britain are vested in the Coal Authority under the Coal Industry Act 1994. Entering or disturbing them requires the Authority's permission, and that includes drilling through a coal seam during site investigation, grouting workings, piling into or through a seam, and any works to a mine entry.

Practical points:

• Apply for the permit in parallel with, not after, the planning application, because investigation results usually feed the design.
• The permit is separate from planning permission and from Building Regulations approval. Permission for the development does not authorise disturbance of coal.
• Where a mine entry is being treated, expect the Authority to want the methodology and the verification records.

Budget the lead time. A site investigation that cannot start until a permit is issued is a site investigation that is not in the design programme where you assumed it was.

Conditions the authority typically imposes

Councils in coalfield areas tend to use a familiar sequence of conditions, and knowing the shape of it helps you programme around it:

1. No development until a scheme of intrusive site investigation has been submitted and approved.
2. The investigation carried out and a report of findings submitted, with any necessary remediation scheme approved before the affected part of the development starts.
3. Remediation carried out, followed by a verification report confirming what was done.
4. Gas protection measures installed and verified where mine gas is identified, designed to the relevant characteristic situation.
5. Reporting of any unexpected mining feature encountered, with work stopped in that area until it is dealt with.

Where ground gas or contamination is involved, the council will expect reports prepared in accordance with the relevant British Standards by suitably qualified and experienced people, and a contaminated land assessment sits alongside the mining work rather than replacing it. Both are areas where professional input is a legal and practical necessity rather than a preference.

Basements in coalfield areas compound every issue at once: deeper excavation into workings, gas ingress risk, groundwater and neighbour impact. Where a basement is proposed, a Basement Impact Assessment and the construction management questions covered in construction management plans for basement excavation belong in the same conversation as the mining risk.

Non coal mining legacy

The framework above only exists for coal. Other mining legacy is just as capable of stopping a scheme and has no equivalent central body or published risk mapping.

The main ones to think about:

• Tin, copper and china clay in Cornwall and Devon, where shafts and adits are numerous and often unrecorded.
• Lead and fluorspar in the Derbyshire Peak and the northern Pennines.
• Chalk and limestone mines and deneholes in Kent, Surrey and parts of London and the Chilterns.
• Salt and brine subsidence in Cheshire, which has its own compensation arrangements.
• Ironstone in Northamptonshire and Lincolnshire, and gypsum in Nottinghamshire and Cumbria.

For these, the desk study draws on British Geological Survey records, historic mapping, mineral planning authority records, local museum and mining society archives and site walkover evidence. There is no referral area to check, which means the risk has to be identified by whoever scopes the ground investigation. On a site in a historic mining district, ask the question explicitly rather than waiting for it to appear in a borehole log.

This is general guidance, not legal advice. Ground conditions and record accuracy are site specific, so check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required.

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