Ground investigation in Wigan.
Wigan is home. Our office and rigs are based here, and we know the borough's ground: coal measures and old shallow workings in the north, sandstone in the south, and glacial clay over most of it.
- Bedrock
- Coal Measures north, sandstone south
- Superficial
- Mostly glacial till
- Coal legacy
- Shallow workings, poor records
- Also watch for
- Colliery spoil, peat near Astley
The ground under Wigan
What we usually find.
Every site is different, and regional geology is only ever a starting point. These are the conditions we typically plan for across the borough.
- Two kinds of bedrock. Carboniferous Coal Measures (sandstone, mudstone and coal) lie north of a line from Ashton-in-Makerfield to Boothstown. To the south, the rock is mainly weaker Permo-Triassic sandstone. Hindley, Ince and Standish sit on the Coal Measures; Leigh, Golborne and Astley are close to the line, so it's worth checking which side a site falls.
- Glacial till over most of the borough. The till is generally dense and stiff. About half the borough has less than 5m of these deposits, but old buried channels in the bedrock locally hold more than 50m.
- A long coal mining history. Around 50 colliery companies were working in and around Wigan by about 1900, and the last deep mine, Bickershaw near Leigh, closed in 1992. Much of the early shallow mining has poor or missing records, mostly across the northern two-thirds of the borough.
- Colliery spoil and industrial fill. Made ground is often colliery spoil, and the borough's industry included foundries, brickworks, engineering and railway depots, with many former landfill sites.
- Peat in the south-east. Around Astley and Chat Moss, water-filled peat can be thick and very compressible.
What it means for your project
How we plan for it.
On the Coal Measures, we check the site against the Mining Remediation Authority's (formerly the Coal Authority) records first. Parts of the borough lie within its Development High Risk Area, where new development needs a coal mining risk assessment, and where that points to possible shallow workings, rotary drilling is the usual way to find them. Drilling into coal or old workings needs an MRA permit, which we build into the programme.
Where the till is thick, cable percussion boreholes take us through it to firmer ground or rockhead, with samples and tests as we go.
On spoil, fill and former industrial land, we sample for contamination alongside the geotechnical work.
For extensions and smaller sites, a trial pit or window sample is often enough, plus a soakaway test if your drainage needs one.
FAQs
Wigan questions.
Is my Wigan site in a coal mining risk area?
Parts of Wigan lie within the Mining Remediation Authority's Development High Risk Area, but it's a patchwork, not the whole borough. You can check an address on the MRA's free interactive map, or send us the address and we'll check it as part of your quote.
Do you cover Leigh, Hindley, Standish and the rest of the borough?
Yes. We're based in Wigan and work right across the borough, from Standish to Leigh and Golborne to Astley.
Do I need drilling for coal workings for a house extension?
Not usually. Householder extensions are generally treated differently from new development, but it depends on the site and your local planning authority. Our guide on coal mining risk assessments explains more.
Sources
British Geological Survey, A geological background for planning and development in Wigan (1995). Wigan Council, Contaminated Land Strategy (2015). Mining Remediation Authority, coal mining information and permits.