Ground conditions are the costs nobody budgets for. The ground conditions and contamination map holds what is already below a site, and what that ground is protecting.

Historic landfill

21,733 closed landfill sites in England, with the Welsh register alongside. These are sites that stopped taking waste, often decades ago, frequently before any requirement to record what went into them.

It is the highest-value layer on the map for anyone buying land, and the one most likely to be missing from a site's own history. Development over historic landfill is not prohibited; it is expensive, and the expense arrives after exchange if nobody looked.

Extraction and mining

11,640 quarries and extraction sites, 3,253 mineshafts, 46 closed mining waste facilities and 2,124 onshore petroleum wells. Britain's industrial history is unusually well documented and unusually widely distributed.

What the ground protects

Underneath all of it: 271 groundwater bodies, 450 drinking water protected areas, 148 safeguard zones, 600 nitrate vulnerable zones and 21,593 private water supplies. These are the reason contamination is regulated rather than merely undesirable.

Source protection zones in particular change what may be done on a site regardless of who owns it, and they are drawn from where water travels underground rather than from anything visible on the surface — so they rarely align with any boundary a buyer would otherwise be looking at.

Sources

Environment Agency (historic landfill, permitted waste sites, nitrate vulnerable zones, groundwater bodies, drinking water protected areas and safeguard zones), Natural Resources Wales, SEPA and the British Geological Survey, under the Open Government Licence.