Coal mining risk areas and the referral you cannot skip

If your site falls inside a Development High Risk Area, a coal mining risk assessment is almost certainly on the council's local validation list, and the application will sit unvalidated until you provide one. The coalfield covers a large part of northern England, the Midlands, the North East, Kent and parts of the South West, and the high risk layer marks where recorded mine entries, shallow workings or other hazards sit close enough to the surface to affect development. The referral is not optional and it is not a formality.

The layer is published by the Coal Authority, now operating as the Mining Remediation Authority, and it is reproduced on many council constraint maps. Check it before you exchange contracts, not after.

What the high risk area layer actually shows

The coalfield is split into two zones. A Development Low Risk Area covers most of it. A Development High Risk Area covers the smaller part where one or more recorded hazards are present, which can include mine entries such as shafts and adits, recorded or probable shallow coal workings, mine gas, spoil heaps, surface hazards from past opencast working, or recorded subsidence claims.

Being in the high risk area does not mean the site is undevelopable. It means a hazard is recorded near enough to matter and that somebody has to establish whether it affects the proposed building footprint. Plenty of houses are built on high risk sites every year after grouting or a redesigned foundation.

The layer is a screening tool built from records. Records of nineteenth century working are incomplete, so a low risk designation is not a statement that no workings exist. Our note on using the coalfield interactive map before you buy a site covers the search itself.

When the assessment becomes a validation requirement

Coalfield authorities generally place a coal mining risk assessment on their local list for applications in a high risk area, usually excluding householder applications and minor works that do not involve new foundations or ground disturbance. The exact scope differs, so read the council's published local list rather than assuming.

The Mining Remediation Authority operates standing advice for planning authorities and comments on applications in high risk areas. Where the assessment shows a hazard affecting the development, the standard outcome is a recommendation for conditions requiring intrusive investigation and any remediation before development starts.

An assessment written by someone with no ground engineering background tends to get a holding objection. The document has to interpret the mining records against the proposal, not just reproduce them, so it belongs with a geotechnical specialist. A Geotechnical Assessment and the coal mining risk assessment are often prepared together and cross-refer.

Mine entries, shallow workings and zones of influence

A mine entry is the sharpest constraint on a small site. Shafts were frequently backfilled with whatever was to hand and capped in ways that would not be accepted now, and the ground around the entry can be disturbed well beyond the shaft lining.

A zone of influence is applied around each recorded entry, derived from the shaft dimensions, the depth of unconsolidated deposits above rockhead and the geology. Its radius is a calculation rather than a fixed figure, so treat any rule of thumb you are given with suspicion. Recorded positions are also approximate, sometimes by tens of metres, which is why the zone is precautionary and why locating the entry on the ground is part of the investigation.

Shallow workings raise a different question. The concern is the thickness and competence of the rock between the worked seam and the foundation, and whether voids or partially collapsed workings remain. Where the cover is thin, treatment usually means drilling and grouting the workings across the footprint plus a margin.

Ordering the report and reading it

Buy the mining report early, because it costs far less than a week of programme. A basic report gives the recorded features. An interpretive or consultants' report adds the plans of the seams and workings that the assessment needs.

When the report arrives, look for these entries before anything else:

1. Recorded mine entries within or near the site boundary, with their stated accuracy.
2. Seams worked, their depth, and whether working was recorded as shallow.
3. Probable unrecorded shallow workings flagged over any part of the site.
4. Mine gas records, past hazard reports and any subsidence claims.
5. Present or future underground working licences and opencast areas.
6. Whether the site lies in a surface hazard or tip area.

Then plot the features against the proposed layout at the same scale. A shaft 3 metres outside the plot boundary still has a zone of influence that may cross it.

Intrusive investigation and permission to disturb coal

Drilling into coal seams, workings or a mine entry requires permission from the Mining Remediation Authority under the Coal Industry Act 1994, because the coal and the mines remain in public ownership. Grouting works need the same permission. The application is straightforward, and it takes time, so build it into the programme rather than discovering it the week the rig is booked.

Investigation on a small site usually means a small number of rotary open hole or rotary cored boreholes positioned on the footprint and on any zone of influence, with grout takes recorded. Where mine gas is a concern, monitoring wells and a period of gas monitoring follow, assessed against the ground gas guidance in CIRIA C665 and the protection measures in BS 8485. That work overlaps with a Contaminated Land Assessment where the site has a further industrial history.

Conditions and what has to be discharged

Expect a condition in three parts. An intrusive site investigation scheme to be submitted and approved, the investigation and any remediation to be carried out before development begins above a defined level, and a verification report to be submitted before occupation.

Verification is where schemes stall. The report needs grout records, borehole logs, as-built positions and a statement signed by the engineer that the ground has been treated as designed. Assembling that afterwards from a contractor's paperwork is far harder than recording it as the work proceeds.

Low risk sites that still need attention

A low risk designation removes the validation requirement in most authorities. It does not remove the ground risk, and three situations deserve a second look.

Sites near the edge of the coalfield, where recorded workings stop abruptly at the limit of the records rather than at a geological boundary. Sites with spoil or tip material on or adjacent to them, which raises settlement and combustion questions outside the mining layer altogether. And sites with a recorded surface hazard such as an old drift entrance close by.

Conveyancing searches often reveal features that the planning constraint layer does not, so compare the two. And where the ground investigation for foundations is happening anyway, the extra cost of asking the driller to record coal and void encounters is small.

This is general guidance, not legal advice. Coal mining risk assessment and ground investigation are work for suitably qualified and experienced engineers, and for specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.