You will learn
What could stop the work, or hurt someone?
You now know what the site used to be, what the ground is made of and where the water is. This lesson covers the rest: the things that limit what, when and how you can work, and the hazards hidden in the ground that could harm people.
- Tell the difference between a constraint and a hazard, and give examples of each.
- Find UK information on nature, heritage, landfill, mining, radon, unexploded bombs and buried services.
- Record each finding with what it means, including any permission or specialist needed before work starts.
Why it matters
Constraints and hazards
Constraints
Things that are protected, so they limit what you can do: wildlife, habitats, historic buildings and archaeology. Get them wrong and the work can be stopped, delayed by a season, or lead to prosecution.
Hazards
Things that could cause harm: ground gas, old mine workings, radon, unexploded bombs and buried cables and pipes. Get them wrong and someone can be hurt.
Both have one thing in common: they are far cheaper to deal with when you know about them before anyone arrives on site. Some need a survey or permission that takes weeks or months to arrange.
The point
The desk study is where constraints and hazards are first written down. If they are not in it, the people planning the investigation and the works may never hear about them.
The idea, in plain words
Constraints: nature and heritage
Sites of Special Scientific Interest (SSSIs) and other designated sites are shown free on Defra’s MAGIC map. Work on or next to them can need consent from the nature conservation body, and may be limited in timing or methods.
FreeBats, great crested newts, badgers and nesting birds are among the species protected by law. Old buildings, trees, ponds and river banks are clues. An ecologist’s survey may be needed, and some surveys and works can only happen at certain times of year.
Clues freeJapanese knotweed is the best known. It is not an offence to have it on your land, but it is an offence to cause it to grow in the wild, and soil containing it that leaves the site is controlled waste. Spreading it can be costly.
FreeListed buildings, scheduled monuments and registered parks are on the National Heritage List for England. Works affecting a scheduled monument need consent. Conservation areas are set by the local council.
FreeEach area has a Historic Environment Record (HER), kept by the local council or its archaeology service. Many can be searched through Heritage Gateway. If a site may have buried archaeology, the council may ask for an archaeologist to watch the digging, known as a watching brief.
Free to searchAsk early: does anyone need to give permission?
In reviews, these questions come up again and again: does any consent or approval need to be in place before the investigation, who applies for it, and does it restrict the machines, the timing or the methods? Will protected species limit working hours or months? Is an archaeological watching brief needed? A desk study that answers them saves weeks.
The idea, in plain words
Hazards in the ground: gas, mining and radon
Landfills, deep made ground, peat and soft organic river deposits can produce methane and carbon dioxide. The Environment Agency’s historic landfill dataset shows known former landfills, but it may be incomplete, so compare it with your old maps.
FreeThe Mining Remediation Authority (formerly the Coal Authority) has a free map viewer. If a site is in a Development High Risk Area, most planning applications need a Coal Mining Risk Assessment. Other mining, and natural cavities, usually need a commercial data report.
FreeRadon is a natural radioactive gas from certain rocks. UKHSA’s radon map shows the chance of high radon levels in homes in each area. Depending on that chance, new buildings may need basic or full radon protection, set out in BRE guidance BR 211 (2023 edition).
Free mapWrite down where the gas could come from
For ground gas, a desk study does not measure anything. It lists the possible sources (a landfill, deep fill, peat, old mines) and how close they are. That tells the investigation where to put gas monitoring wells.
The idea, in plain words
Hazards in the ground: bombs and services
Unexploded ordnance (UXO)
Bombs from the Second World War, and items from military training, are still found on UK sites. The industry guidance, CIRIA C681, sets out a staged approach: a preliminary risk assessment, then a detailed one if needed, then measures on site if the risk calls for them, such as a specialist on site or a survey. Free bomb risk maps give a first indication, but they must never be used on their own to plan work.
Always state the UXO risk, even when it is low
A desk study that says nothing about unexploded ordnance leaves the reader guessing. In reviews, a missing UXO statement is one of the first things to be queried. State the risk, the source of the assessment, and whether anything is needed on site.
Buried and overhead services
HSE guidance (HSG47) says clients must make reasonable enquiries about underground services and pass the information on. In a desk study, that means collecting the utility companies’ records for water, sewers, gas, electricity and telecoms, and noting overhead power lines.
Records are not the ground
Utility records can be incomplete, and old or abandoned pipes are the easiest to miss. Ask the client about current and abandoned pipes and cables, say clearly that records may not show everything, and recommend a services survey before any digging.
Wherever you are
Hazards the UK rarely sees
Some ground hazards are rare in the UK but common elsewhere. If you work outside the UK, check for these too:
Swelling clays
Clays that swell when wet and shrink when dry, cracking buildings and roads.
Collapsible soils
Dry, loose soils that suddenly settle when they get wet.
Sinkholes
Holes that open where limestone, chalk or gypsum dissolves underground.
Landslides
Especially on steep slopes in deeply weathered ground after heavy rain.
Coastal erosion
Cliffs and shorelines retreating year by year.
Earthquakes
Shaking, and loose wet sands that can lose their strength during it.
Where to look
National geological surveys often publish hazard maps. Look at the landscape too: cracked walls nearby, steep slopes, hollows in the ground and local knowledge are all clues. If a hazard is common in your region, your country’s standards will usually say how to deal with it.
On our site
Brindlemere Yard: constraints and hazards
A table works well for this section. Every row ends with what it means.
Brindlemere Yard: Desk Study Report (fictional example)
5. Constraints and hazards
| Topic | Finding | What it means |
|---|---|---|
| Protected sites | None within 1 km | No consent needed for this |
| Protected species | Old sheds, mature trees and the river bank could support bats and nesting birds | Ecologist’s survey before demolition or clearance; clearance timed outside the nesting season |
| Invasive plants | Dense vegetation along the river on aerial images | Check for Japanese knotweed on the walkover |
| Heritage | The former corn mill 200 m north is a listed building. No scheduled monuments. Not in a conservation area | No direct effect on the site; consider vibration if piling |
| Archaeology | The HER records the 19th-century iron works | The council may ask for a watching brief |
| Landfill and gas | The former refuse tip 150 m south is in the historic landfill dataset. Made ground and soft river deposits on site | Ground gas monitoring needed |
| Mining | Outside the coalfield. No other mining recorded | No further action |
| Radon | In the lowest band on the radon map | No radon protection needed |
| UXO | Bomb risk map shows low risk for the area, but the iron works was an industrial site during the Second World War | Preliminary UXO risk assessment by a specialist before intrusive work |
| Services | Water main and sewer under the access road. Electricity cable across the north-west corner. Overhead power line along the western boundary. Records do not show the works’ old pipes | Services survey before digging; assume old pipes may remain; keep plant clear of the overhead line |
Notice the UXO row
The map says “low”, but the site history adds a reason for caution. A good desk study joins up evidence from different parts of the study, rather than copying each source on its own.
Your turn
Build your constraints and hazards table
Wherever you are
Look for your country’s protected sites and species, its register of historic sites, records of old landfills and mines, any natural gas or radon maps, the risk of old military explosives, and utility records. Where no records exist, say so, and lean on the walkover and on local knowledge.
Task (25 minutes)
For your own site, make a table with three columns, Topic, Finding and What it means, covering:
- Protected sites, protected species and invasive plants.
- Heritage and archaeology.
- Landfill and ground gas, mining, and radon.
- Unexploded ordnance.
- Buried and overhead services.
Then underline anything that needs a permission or a specialist before the investigation starts.
Quick check
Five quick questions
This is not a test. It simply shows you whether you are ready for Lesson 6. Choose an answer to see the explanation.
Key points
What to take away
- Constraints protect something (nature, heritage). Hazards could harm someone (gas, mining, radon, UXO, services).
- Most UK constraint and hazard information is free: MAGIC, the National Heritage List, local HERs, the historic landfill dataset, the mining map viewer and the radon map.
- Find out early whether any permission, survey or specialist is needed before the investigation.
- Always state the UXO risk, even when it is low.
- Utility records are not the ground. Ask about abandoned pipes and recommend a services survey.
Where to look (free)
- MAGIC map, for protected sites (Defra)
- National Heritage List for England (Historic England)
- Heritage Gateway, for Historic Environment Records
- Historic landfill sites (Environment Agency)
- Free coal mining information (Mining Remediation Authority)
- UK radon maps (UKHSA)
- HSG47: Avoiding danger from underground services (HSE)
Up next: Lesson 6
The site walkover. Planning the visit, staying safe, what to look for, and what to do when records are missing.