Finding borehole and ground data before you buy a plot
Published borehole records and geological mapping cost nothing and answer most of the ground questions a desk study has to raise. Here is how to search them.
A borehole records site check starts with the British Geological Survey's onshore map viewer, where you can search by location for logged boreholes, shafts and wells, view the bedrock and superficial deposits mapping, and in many cases open a scanned copy of the original driller's log. For a single plot it takes half an hour and tells you whether the ground beneath the site is clay, sand, made ground or something that needs a specialist. That is enough to decide whether you need an intrusive investigation before you submit, or whether a condition will do.
None of it replaces site investigation. It does stop you commissioning the wrong investigation.
Searching for boreholes near a site
Open the onshore viewer, zoom to the site and switch on the borehole layer. Records appear as points, each with a reference, a depth, a date and an indication of whether a scan is available.
Three habits make the search useful rather than decorative.
Search a radius rather than the site itself. Boreholes on your plot are rare. Records within a few hundred metres on the same geological unit are what you are looking for, and a cluster from a nearby road scheme or housing estate is often the best data available.
Read the depths before the logs. A 3 metre hand-dug trial pit from 1972 tells you about the topsoil and nothing else. A 25 metre rotary hole from a bridge investigation tells you about the bedrock.
Note the date and the purpose. Boreholes sunk for water supply, for mineral prospecting and for foundation design record different things, and a water well log may skip the detail of the first few metres entirely.
Some records are confidential, which means the metadata is visible and the log is not. The point is still useful, because it confirms that somebody drilled there and what depth they reached.
Reading a borehole log
A log is a strip description of what came out of the hole, with depths down the left. Older logs are handwritten and use the driller's own vocabulary. Logs prepared since the 1980s generally follow the soil and rock description conventions in BS 5930.
Work down it looking for five things.
- Made ground. Any description mentioning brick, ash, clinker, concrete, slag or "fill" is made ground, and it raises both a geotechnical question about bearing capacity and a contamination question about what is in it.
- The depth to competent natural strata, which is what the foundation design will key into.
- Water strikes, recorded as a depth and often with a rest level. A strike at 1.5 metres changes the whole basement conversation.
- Cohesive versus granular description. Firm clay and loose sand behave differently under a strip footing and drain very differently.
- Any note of organic material, peat or soft alluvium, which usually means a settlement problem.
Strength data appears as standard penetration test blow counts or undrained shear strength values. You do not need to interpret them, but noting that they exist means your engineer gets something to work with.
Geological mapping and superficial deposits
The viewer also shows mapped bedrock and superficial deposits. The distinction matters because the superficial layer is what most domestic foundations sit in.
Look up the named unit rather than the colour. A unit described as glacial till behaves differently from river terrace gravel, and alluvium next to a watercourse is both weak and usually wet. Shrinkable clay units drive foundation depth and tree proximity decisions under the relevant Building Regulations guidance, which is why a mapped London Clay or Lias Group site needs a different foundation assumption from a sandstone site.
The viewer carries separate layers for artificial ground, mass movement and linear features such as faults. Artificial ground mapping is coarse and conservative, so treat it as a prompt to look at historic maps rather than as a finding. Our note on historic maps as former land use evidence covers the follow-up.
Ground stability hazard datasets cover shrink-swell, compressible ground, collapsible deposits, landslides, running sand and soluble rocks. They are indicative at a national scale and are sold as screening products rather than site findings, so quote them as screening.
Mining, shafts and the records that sit elsewhere
Coal mining sits outside the geological viewer. In a coalfield referral area the authority will expect a coal mining risk assessment, and the mine entry and workings data comes from the Coal Authority rather than from the geological survey. Shafts, adits and recorded mine entries carry a standing advice buffer, and a site with a recorded entry inside or near it needs specialist input from the outset.
Non-coal mining matters too. Chalk and clay extraction, ironstone, gypsum, salt and building stone have all left voids under English towns, and the records for those are patchy and local. The authority's own records, the historic environment record and old maps often fill the gap.
Where mining or ground stability is in play, a geotechnical assessment prepared against Eurocode 7 is the document the authority will expect, and councils usually look for a suitably qualified author.
Using the data in a desk study
A planning desk study has two purposes, and the same borehole data feeds both.
For contamination, the preliminary risk assessment follows the Environment Agency's land contamination risk management framework and establishes a conceptual site model of sources, pathways and receptors. Made ground in a nearby log, a water strike at shallow depth and a former industrial use on an old map together tell you whether a Phase 2 investigation is likely. Land contamination reports are expected to be prepared in accordance with BS 10175 by suitably qualified and experienced persons, and that expectation is a legal one for this work, so a draft is a starting point for that professional rather than a substitute. A contaminated land assessment is the report type the authority's validation list will usually name.
For geotechnical purposes the desk study informs the scope of investigation: how deep to go, whether cable percussion or rotary drilling is appropriate, how many positions, and whether groundwater monitoring is needed. Where a basement is proposed, the same data drives the basement impact assessment, and a shallow water strike will dominate it.
Cite what you used. Reference the borehole numbers, the mapped units and the dates of the records in the report, so a reviewer can repeat the search.
Ordering scans and dealing with absence
Many scanned logs open directly in the viewer. Others have to be ordered, and the survey operates a service for retrieving records that have not been digitised. Allow time, because a request against a paper archive is not instant.
Sometimes there is nothing. Rural sites, upland sites and recently developed greenfield land often have no records within any useful distance.
But absence of data is a finding in its own right, and the desk study should say so rather than papering over it. State the search radius used, and let the absence drive a proportionate investigation rather than an assumption. On a single plot that might be three trial pits and a soakaway test. On a 40-unit scheme it will be more.
One honest uncertainty worth naming: published records describe what the driller saw at one point on one day, and ground conditions vary across a plot more than people expect. A log 50 metres away showing 1 metre of made ground is not a guarantee about your foundation trench.
Enter your postcode on PlanScope to see which of the 66 reports your site is likely to need.
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.
Frequently asked questions
Are borehole records free to view?
Many scanned logs can be viewed without charge through the British Geological Survey's onshore map viewer, and the point data showing location, depth and date is openly available. Some records are marked confidential, so only the metadata is shown, and undigitised records have to be requested through the survey's enquiry service.
How far from my site should I search for boreholes?
Start with a few hundred metres and widen until you find records on the same geological unit. Boreholes on a small plot are rare, so nearby clusters from road, bridge or housing investigations are usually the best available data. Record the radius you searched so the desk study can be repeated.
Does a desk study remove the need for ground investigation?
No. A desk study scopes the investigation and can sometimes justify a lighter one, but it describes conditions at other points rather than on your site. Where made ground, a shallow water strike or a former industrial use appears, intrusive work is almost always needed before a foundation or remediation design can be fixed.
Where do I find coal mining information?
From the Coal Authority rather than the geological survey. In a coalfield referral area the planning authority will expect a coal mining risk assessment, and recorded mine entries carry buffer zones that trigger specialist input. Non-coal mining records are patchier and often sit with the local authority or the historic environment record.
What does made ground in a log mean for my application?
It raises two separate questions. Geotechnically, made ground usually has poor and variable bearing capacity, so foundations may need to go deeper or be redesigned. For contamination, it means the material has to be characterised, because what was tipped determines whether a Phase 2 investigation and remediation are needed.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.