Ground risk is one of the most underestimated challenges in property development. Here are the nine principal geohazards that affect development sites across England.

1. Mining Legacy

Former coal mining, salt extraction, ironstone, and other mineral workings can leave voids, subsidence features, and unstable ground. The MRA designates high-risk areas — sites within a Development High Risk Area (DHRA) require a Coal Mining Risk Assessment before planning can be granted.

2. Compressible Ground

Soft deposits such as peat, alluvium, and made ground can cause long-term settlement under load. Relevant for valley floors, riverside locations, and brownfield land.

3. Shrink-Swell Clays

Clay soils expand when wet and contract when dry — cracking foundations and damaging structures. London Clay, Gault Clay, and similar high-plasticity formations carry significant risk.

4. Slope Instability

Sites on or near slopes may be susceptible to landslides, shallow failures, or creep. Particularly relevant in upland areas, coastal cliff settings, and valley sides.

5. Dissolution Features

Chalk, limestone, gypsum, and salt are soluble rocks. Dissolution can create cavities, sinkholes, and subsidence — sometimes without warning. The Lias Group, the Chalk of southern England, and gypsum-bearing Permian rocks of the north-east all require careful assessment.

6. Made Ground

Artificial fill — demolition rubble, colliery spoil, industrial waste — is common on brownfield sites. Made ground can be variable, compressible, and potentially contaminated.

7. Flood Risk

The EA’s Flood Map for Planning identifies three flood zones. Development in Flood Zones 2 and 3 requires a Flood Risk Assessment and sequential/exception testing.

8. Radon

A naturally occurring radioactive gas. BGS mapping identifies radon-affected areas across England — Class 3 and above may require protective measures under BR 211:2015.

9. Ground Gas

Methane and carbon dioxide can be generated by decomposing organic material, landfill sites, and coal-bearing geology. Assessment required where a site is near a landfill, on made ground, or underlain by coal measures.

— Tristan Morgan BSc(Hons) EurGeol CGeol FGS AMICE, UK Registered Ground Engineering Specialist, Director of Magnum GSI Ltd