Documents for a scheme over a disused mine shaft

A recorded mine entry on a development site brings an exclusion zone, a treatment design, a permit from the Coal Authority or the relevant mining remediation body for intrusive works, and a condition sequence that has to be discharged before anything is built over it. The exclusion zone is set from the position of the shaft or adit plus an allowance for the uncertainty in that position, and on a small site it can swallow the plot. Establishing where the entry actually is, rather than where the plan says it is, is the first and most expensive piece of work.

This is not the same exercise as a coal mining risk assessment for a site that merely sits in a development high risk area. Here there is a known entry, and the question is treatment.

Establishing the position and condition of the entry

Recorded positions come from mine abandonment plans, and those plans were drawn to varying standards. A position quoted to the nearest metre may carry an uncertainty of 10m or more, and some entries are recorded only as approximate.

The investigation sequence that works runs from records to ground:

• Mining records search covering abandonment plans, shaft registers, previous investigation reports and any records of earlier treatment.
• Historic mapping to look for headgear, spoil heaps, tramways and buildings that indicate the working position.
• Walkover survey recording depressions, vegetation changes and any capping visible at the surface.
• Geophysical survey to narrow the search area before excavation.
• Intrusive investigation, usually trial pitting or probe drilling on a grid, to locate the entry and establish the condition of any existing cap.

The deliverable is a plan showing the entry position, the confidence in that position and the condition of any treatment found. That plan drives everything else, and submitting a layout without it tends to produce a condition requiring the layout to be revised.

The exclusion zone and layout consequences

An exclusion zone is applied around the entry, scaled to the shaft diameter and the uncertainty in its position, with no buildings permitted inside it until the entry is treated and the treatment verified.

Three layout responses are in general use. Place the zone within open space, parking or landscape so no dwelling sits over it. Treat the entry so a reduced zone or none applies, which needs the treatment design approved first. Or, where the entry cannot be located with confidence, keep the whole uncertainty envelope free of development.

The commercial point is that an untreated entry in the middle of a developable plot removes units. Work out the net developable area after the zone before the land deal, because the figure rarely improves later. Our note on documents for a site crossed by a public sewer covers the equivalent arithmetic for an easement.

Treatment options and who approves them

Treatment is engineering design, and it is approved by the mining remediation body rather than by the local planning authority, even though the planning condition requires it.

Building over a treated entry is sometimes possible with a designed cap and a verified position, and sometimes refused outright. Ask the question early, because the answer determines the layout rather than the other way round.

Permit requirements for intrusive works

Entering, disturbing or drilling into coal workings or a mine entry needs a permit from the body responsible for the coal authority functions, and carrying out the work without one is an offence. The permit covers investigation as well as treatment, so the probe drilling used to locate the entry needs it too.

Allow time. A permit application requires the method statement, the drilling or excavation positions, the contractor's competence and the proposed grout or backfill specification, and it is assessed rather than issued on request. A contractor who has done this work before will usually hold the relationship and the templates, which is worth more than a lower day rate.

Where the site is in a gas risk area as well, the investigation and the permit should cover both purposes in one visit, since mobilising a rig twice is pure cost.

Gas monitoring and protection measures

Mine entries and shallow workings are a ground gas pathway, so monitoring normally runs alongside the location work. Methane and carbon dioxide are the gases of concern, with oxygen depletion recorded as part of the same regime.

The monitoring regime has to be long enough to capture falling atmospheric pressure, which is when gas emission peaks. Several rounds across a period of weeks, with barometric pressure recorded at each visit, is the expectation, and a single visit will be rejected.

The output is a characteristic situation classification and a protection design, which may include a gas resistant membrane, a ventilated subfloor void and the vent on the shaft cap. That work sits with the contaminated land assessment stream, and a licensed or suitably qualified and experienced person has to prepare it: these reports are expected to follow the relevant British Standard and a PlanScope draft is a starting point for that professional rather than a substitute.

Interaction with foundation and drainage design

Two design consequences follow the treatment, and both are easier to resolve early.

Foundations near a treated entry have to bear on ground unaffected by the shaft collar and its disturbed zone, which often means piling or a raft where a strip footing would otherwise do. A geotechnical assessment covering the workings, the collar and the backfill is the document that resolves it.

Drainage is the one people miss. Infiltration drainage near a mine entry or shallow workings is normally unacceptable, because water routed into workings can mobilise fines, cause subsidence and create a pollution pathway. That removes the top option from the discharge hierarchy and pushes the scheme towards attenuation and a positive outfall, which the Drainage Strategy has to show with the reasoning stated.

The pack and the condition discharge sequence

The application material and the conditions follow the same logic, and proposing the sequence yourself usually produces more workable wording than waiting for the officer's draft.

1. A coal mining or mine entry report with the records search, the recorded position, the uncertainty and the proposed investigation.
2. A site layout showing the entry, the exclusion zone and the development kept clear of it.
3. A phase 1 ground conditions report covering gas, contamination and stability.
4. A proposed investigation and monitoring method statement, including the permit requirement.
5. A statement of the treatment principle, even where the design will follow.
6. Drainage proposals that avoid infiltration in the affected area.
7. A verification strategy setting out what will be submitted to close the conditions.

Expect conditions requiring the investigation and treatment scheme to be approved before development begins, the treatment to be carried out and verified before any building above ground, and a verification report before occupation. Where gas protection is required, a separate verification of the installed membrane is usual.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to see which documents a site with mining constraints is likely to need.