Ground investigation in Lancashire.
North of Wigan, the ground changes from the Lancashire coalfield around Chorley to boulder clay plains and the Ribble valley around Preston. We investigate both.
- Bedrock
- Coal Measures, grit, Sherwood Sandstone
- Superficial
- Boulder clay with sand and gravel
- Coal legacy
- Mainly Chorley and the south-east
- Also watch for
- Ribble alluvium and estuary soils
The ground
What we usually find.
Chorley, Coppull and Adlington
- Part of the Lancashire coalfield. Lower Coal Measures, mudstones and shales with sandstone and many coal seams, lie mainly around Chorley, Heskin and Euxton, with Millstone Grit to the east around Anglezarke and Rivington and Permo-Triassic rocks on the low ground to the west.
- Recorded old workings, for example in the Holcombe Brook Coal south-west of Chorley. The Mining Remediation Authority says recorded mining features in Central Lancashire are concentrated in the south-east of the area.
Preston and the Ribble
- Sandstone and mudstone under glacial cover. Preston's old town stands on a ridge of Sherwood Sandstone above the Ribble, and boulder clay covers much of the plain, with widespread glacial sands and gravels between clay layers.
- River and estuary soils. Alluvium and tidal flat deposits line the Ribble, Douglas and Darwen valleys.
What it means for your project
How we plan for it.
Around Chorley, Coppull and Adlington, many sites need a coal mining desk check, then rotary drilling for shallow workings where the site is in the Development High Risk Area.
On the boulder clay plain, boreholes through clay with sand and gravel lenses are the norm, with careful sampling where the layers change.
Near the Ribble, softer river and estuary soils need extra care, often with deeper boreholes.
On rural plots, a percolation test tells you whether a septic tank or treatment plant drainage field will work.
Sources
British Geological Survey, Geology of the country around Preston (1963). Mining Remediation Authority, representation to the Central Lancashire Local Plan (2025). Winckley Square Preston, What lies beneath.