Checking coal mining and former mineral workings

A coal mining report site check starts with a free map search. The national coal mining regulator, the body long known as the Coal Authority, publishes a search that tells you whether a site falls within a development high risk area. If it does, expect the local planning authority's validation checklist to require a coal mining risk assessment with the application, and expect the regulator to be consulted. If it does not, the matter is usually closed with a short paragraph in the planning statement.

Two minutes of searching can reshape a programme by several months. Do it before you instruct an architect, not after.

Finding whether a site is in a referral area

The regulator's online search takes a postcode, an address or a grid reference and returns the site's status against the development high risk area layer. That layer is drawn from recorded shallow workings, mine entries, areas of past opencast working and other features the regulator considers material to new development.

Three things to get right at this stage. Search the whole red line, including access land and any off-site drainage, because risk areas have hard edges and a site can be partly in and partly out. Keep a dated screenshot or the reference the search generates. And remember that the layer records what is known, so a site outside it is lower risk rather than no risk.

Where the site is in a high risk area, the council will usually also want to see that the regulator has been engaged. Some authorities ask for evidence of the consultation outcome at validation.

What the standard report covers

A mining data report is a factual search. It typically sets out recorded underground workings beneath or near the site and the seams involved, mine entries such as shafts and adits within a defined distance of the boundary, past and proposed opencast sites, recorded coal mining subsidence claims, recorded mine gas incidents, and whether the land is within an area of surface hazard or a licensed coal operation.

What it does not do is interpret any of that for your scheme. The regulator and the planning authority both distinguish between the data and the assessment, and a submission that attaches the report without interpretation will be returned.

A coal mining risk assessment takes the report and does three things: identifies the hazards relevant to the proposed development, judges whether they are credible given the depth, seam thickness and ground conditions, and sets out what investigation or treatment the scheme needs. Councils usually expect a suitably qualified author, and the assessment normally sits within or alongside a Geotechnical Assessment prepared to the relevant design standards.

Shafts, adits and shallow workings

Three hazard families turn up repeatedly.

Shafts and adits are point hazards with high consequence. A shaft whose recorded position carries a wide tolerance has an influencing zone around it, within which foundations and buildings are usually avoided or specifically designed. Recorded positions from nineteenth-century plans are frequently out by metres, which is why the investigation has to locate the feature rather than assume the record.

Shallow workings create the risk of collapse at the surface, sometimes appearing as a crown hole. Depth of cover relative to seam thickness is the usual screening measure, and below a threshold the ground is treated as potentially unstable and grouted.

Mine gas is the hazard that engineers brief least well. Workings and shafts can act as pathways for methane and carbon dioxide, and oxygen-depleted air is a real risk in confined spaces. Gas monitoring over a period covering falling atmospheric pressure, and then gas protection measures designed to the relevant British Standard for gas protection in new buildings, is the normal response. That work overlaps with the contamination assessment, where a suitably qualified and experienced person is required and the draft is a starting point for them rather than a substitute.

When the authority consults the regulator

For applications within a development high risk area, the authority normally consults the regulator, which responds either with no objection, with a holding objection pending a risk assessment, or with comments on the assessment submitted.

A holding objection is not a refusal and is lifted once adequate information is provided. It does stop the clock in practical terms, because an authority will rarely issue a decision over an unresolved objection from a statutory body of this kind. Submitting the risk assessment with the application avoids the delay entirely.

Where the assessment concludes that intrusive investigation is needed, authorities often accept a condition requiring the investigation and any remediation before development begins, rather than requiring it up front. Ask about that at pre-application stage, because it can save a season.

Risk assessment and remediation options

Treatment depends on the hazard.

• Shallow workings are usually treated by drilling and grouting on a grid, with grout take recorded hole by hole.
• Shafts are located, capped with a reinforced concrete plug or raft designed for the purpose, and a no-build zone is maintained around them.
• Adits and drifts may be plugged or bridged.
• Where treatment is impractical, the layout is redesigned to avoid the feature, with the zone given over to parking, landscape or drainage.
• Gas risk is managed through membranes, ventilated sub-floor voids and, where needed, passive or active venting.

Avoidance costs less than treatment, which is an argument for doing the ground work before the layout is fixed rather than afterwards. A scheme that puts the only workable house plot directly over a shaft influencing zone has created an avoidable problem.

Programme implications of drilling

The sequence is desk study, then an investigation design, then a permit application to the regulator, then drilling, then interpretation, then treatment design, then treatment, then verification. Each step has a lead time and the permit is the one most often forgotten.

Rotary open-hole drilling to prove workings is relatively quick per hole, but the number of holes scales with the area and the grid spacing, and grouting follows separately. Budget for both phases and for the verification report, which is the document that discharges the planning condition and satisfies a lender later.

Historic evidence reduces the drilling. Our note on using historic maps to evidence a former land use explains how successive Ordnance Survey editions pin down former pit heads, tramways and spoil, and our note on reading aerial photography as planning evidence covers post-war imagery, which often shows opencast restoration that the modern map has erased.

Insurance and lender requirements

Coal mining subsidence damage falls within a statutory claims regime administered by the regulator, which is separate from the planning process and from building insurance. For new development, the point that matters commercially is the paper trail.

Keep the data report, the risk assessment, the investigation records, the grouting records with grout takes, the treatment design and the verification report together as one bundle. That bundle is what a purchaser's solicitor, a warranty provider and a lender will ask for, sometimes years later. Where ground gas protection has been installed, keep the validation report for the membrane installation too, because it is routinely requested and rarely available.

Non-coal workings deserve the same treatment with worse data. Where the geological survey records, historic maps or mineral planning authority archives point to chalk mines, deneholes, ironstone, limestone or clay extraction, say so in the assessment and investigate accordingly. An absence of records is not evidence of an absence of workings, and any contamination issues identified should feed into a Land Contamination Phase 1 assessment prepared in accordance with the relevant British Standard by a suitably qualified and experienced person.

This is general guidance rather than legal advice. Check the position with your local planning authority, the coal mining regulator or a qualified professional before relying on it.

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