Using historic mapping to build a site history

A documented site history is the backbone of a contamination desk study, and historic Ordnance Survey mapping is where most of it comes from. Comparing successive editions of the same plot across a century tells you what stood there, what was dug out, what was filled back in and what the neighbours were doing. That chronology drives the conceptual site model, which drives whether intrusive investigation is needed and where the trial pits go.

Get it wrong and the ground investigation looks in the wrong place, which is an expensive way to find out about a filled pond.

Why a documented history carries weight

Planning policy places responsibility on the developer to establish whether land is suitable for its proposed use, with the local planning authority satisfying itself that contamination risks are understood. Councils routinely condition a phased approach: preliminary risk assessment first, then site investigation, then remediation and verification where needed.

The preliminary risk assessment stands or falls on the desk study, and the desk study stands or falls on the history. A report that says the site was "formerly open land" without showing the evidence invites a condition requiring the work to be redone.

Land contamination assessment is work for a suitably qualified and experienced person. National guidance and the relevant British Standard both frame it that way, and a draft prepared without that expertise is a starting point for the professional rather than a substitute for them.

Where the mapping comes from

Ordnance Survey produced successive editions at scales useful for site work from the middle of the nineteenth century onwards. County series mapping at 1:2,500 and six inches to the mile covers most of England from the 1850s, with revisions at intervals thereafter, and National Grid series mapping at 1:1,250 and 1:2,500 follows from the mid twentieth century.

Commercial environmental data reports package the relevant editions with interpretation, and they are the normal route for a professional desk study because they also bundle regulatory datasets. Archive collections of georeferenced historic Ordnance Survey sheets are available online and are useful for a first look at a site you are considering.

Beyond Ordnance Survey there are tithe and enclosure maps held in county record offices, estate plans, town plans, historic aerial photography from the middle of the twentieth century onwards, and the geological and borehole records held by the British Geological Survey. Borehole logs from a neighbouring site are often the single most useful document you can find.

Reading changes between editions

Lay the editions out in date order and work feature by feature rather than impression by impression.

What appears and disappears matters more than what is constant. A pond on one edition and absent on the next means it was filled, and with what is unknown until someone digs. A building present in 1900 and gone by 1938 means a demolition, foundations left in place, and possibly a tank or a pit beneath.

Annotations are the richest source. Ordnance Survey labelled land uses directly, and the vocabulary is consistent across the country: Works, Smithy, Foundry, Tannery, Gas Works, Brick Works, Sand Pit, Old Clay Pit, Quarry (disused), Depot, Refuse Tip, Sewage Works, Mill, Bleach Works. Each carries a set of likely contaminants.

Extend the study beyond the red line. A study area of a few hundred metres around the site catches sources that migrate: a gasworks upwind, a filled quarry upgradient, a tannery discharging to a ditch that crosses the site.

Identifying former industrial uses and what they imply

Match the annotation to the likely contaminants, then check whether the pathway to your proposed receptors exists.

Treat that as a prompt list rather than a conclusion. The contaminants that matter on a particular site depend on the process, the period, the ground conditions and the proposed end use, and a residential garden is a far more sensitive receptor than a warehouse slab.

Infilled ground, ponds and quarries

Filled ground is the finding that most often changes a scheme, because it affects contamination, ground gas and foundation design at the same time.

Work out the extent from the earlier edition, the approximate depth from the feature type, and the fill date from the gap between editions. A clay pit filled in the 1960s with uncontrolled material is a different proposition from a pond filled in 1890 with soil from an adjacent cutting.

Ground gas is the risk people underestimate. Degradable material in fill generates methane and carbon dioxide for decades, and gas protection measures to the relevant standards add cost and buildability constraints to every affected plot.

The geotechnical consequences run alongside. Variable fill produces differential settlement, and a building spanning the edge of a former pit is a classic failure. The Geotechnical Assessment and the contamination work should use the same site history and, ideally, the same investigation.

Feeding the history into the desk study

The history is not an appendix. It is the evidence for the conceptual site model, which sets out sources, pathways and receptors, and which determines what happens next.

1. Build the chronology as a table, one row per map edition, with the date, the scale and what is on the site and within the study area.
2. Identify potential sources from that chronology, with the edition reference for each.
3. Identify receptors for the proposed development: future site users, buildings and services, controlled waters, adjacent land.
4. Identify plausible pathways between them, taking account of geology, made ground and groundwater.
5. State where a source, pathway and receptor are all present, because those are the linkages that require investigation.
6. Set out the scope of intrusive investigation that follows, targeted at the features the history identified.

A Land Contamination Phase 1 assessment is the document that carries all of this, and councils generally expect it with the application where the history or the setting suggests a risk.

Presenting the chronology so it can be checked

Reviewers check the history against their own knowledge of the area, so make it easy.

Include a figure for each map edition used, at a consistent scale, with the site boundary overlaid and the study area shown. Number the figures and reference them in the text. Give the edition dates rather than a vague range, and note where a revision date and a publication date differ.

Where a feature is ambiguous, say so. A rectangle with no annotation on a 1912 sheet may be a building, a tank or a store, and an assessment that admits the uncertainty and recommends a trial pit is more credible than one that guesses.

Other pre-development enquiries fit into the same exercise. Sewer records tell you what crosses the site and where historic discharges went, and ordering sewer records through pre-development enquiries early avoids a late surprise. Historic maps also show routes that may now be recorded rights of way, which is a separate check worth making against the definitive map.

Browse the PlanScope report types to see which ground and contamination documents your site is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Land contamination assessment must be carried out by a suitably qualified and experienced person, and for specialist technical reports qualified professional input may be required.