Geotechnical desk study
A desk review of a site's geology, history, contamination risk and ground hazards, done before any ground investigation.
About this service
A geotechnical desk study is the research stage before anyone digs. It pulls together what is already known about a site: the mapped geology, old maps showing what stood there before, records of nearby boreholes, flood and groundwater information, and any hint of contamination or buried hazards. The aim is to understand the ground well enough to plan a sensible ground investigation, rather than drilling blindly and paying for the wrong tests.
London sites have long and varied histories. A back-garden plot in Southwark might sit over former industrial yards, a site in Newham over old river terrace gravels, and a plot in Barnet on London Clay capped by fill from earlier building. Bomb damage, infilled ponds, lost rivers, old wells and buried foundations all turn up. Knowing about them before the design starts avoids expensive surprises once the contractor is on site.
Our report sets out the expected ground conditions, the likely hazards, and a recommended scope for the ground investigation, including the type, number and depth of exploratory holes. It is the document planning officers usually ask for when a contamination or ground stability condition is attached to a consent. Fees start from £750 + VAT, and the report can be relied on by your designers and the ground investigation contractor.
When you need it
- You're planning a new build, extension or basement
- Planning conditions require a desk study
- You want to scope a ground investigation properly
What's included
- Review of geological maps and records
- Historical maps and site use
- Contamination and ground hazard screening
- Recommendations for investigation
How it works
- Define the schemeWe confirm the proposed development, foundation type if known, any basement and any planning conditions, so the study answers the questions your designers and the council will actually ask.
- Gather recordsWe review geological maps, historical Ordnance Survey editions, available borehole records, groundwater and flood data, and other public records relevant to the site and its surroundings.
- WalkoverWhere useful, we visit to check access for drilling rigs, look for signs of past uses, nearby trees, slopes, watercourses and neighbouring structures, and confirm what the records suggest.
- Risk assessmentWe build a preliminary model of the ground and identify hazards such as shrinkable clay, made ground, soft deposits, groundwater, contamination pathways and potential ground gas.
- Investigation scopeWe recommend the ground investigation needed, with hole types, depths and testing, so it can be priced fairly and gives the data your foundation or basement design really needs.
What you receive
When a desk study saves money on a London project
Skipping the desk study can look like a saving, but it usually moves cost elsewhere. Without it, a ground investigation contractor has to guess the scope, which can mean holes in the wrong place, too shallow for a basement, or missing the contamination testing a planning condition requires. Repeat site visits cost more than getting it right once. The desk study feeds directly into a ground investigation and factual report, and for basement schemes it forms the first part of the screening in a Basement Impact Assessment.
For small single-storey extensions on well-known ground, a full desk study is often more than you need, and a trial pit and foundation inspection may answer the practical questions. The study earns its place on new-build houses and flats, basements, sites with a known industrial past, and plots where planning has imposed a contamination or land stability condition. If you are unsure, our guide to London Clay and foundations is a useful starting point.
Projects that used this service
Frequently asked questions
What is included in a geotechnical desk study?
A typical desk study reviews geological maps, historical maps of the site and its surroundings, nearby borehole records, groundwater and flood information, and indicators of contamination or ground gas. It describes the expected ground conditions, identifies hazards and recommends the scope of a ground investigation. A site walkover is often included to check access and look for visible clues.
Is a desk study the same as a Phase 1 contamination report?
They overlap. A Phase 1 report focuses on contamination risk, while a geotechnical desk study also covers how the ground will behave for foundations and excavations. Many planning conditions ask for a preliminary risk assessment, and a combined desk study can cover both needs. Your council's planning officer can confirm exactly what the condition requires.
Do I need a desk study for a house extension?
Usually not for a straightforward single-storey extension on a well-understood site. Building Control mainly needs to know the soil type, nearby trees and a suitable foundation depth, which a trial pit often provides. A desk study becomes worthwhile for new buildings, basements, sites with an industrial history, or where a planning condition specifically asks for one.
How long does a geotechnical desk study take?
Our typical turnaround is 10 working days, confirmed in writing with the fixed fee before work starts. Some records take time to obtain, and a site walkover needs to fit your access arrangements, so we agree the programme with you at the outset. Starting early helps, because the investigation can be booked as soon as the study is issued.