Phase I & Phase II Site Investigation Costs in the UK (2026 Guide for Developers)

Understanding site investigation costs is an important part of planning any development project. Whether you are preparing a planning application, carrying out due diligence or progressing a site through construction, the scope and cost of a Phase 1 Desk Study and any subsequent site investigation will depend on the characteristics of the site.

A structured approach to site assessment allows potential risks to be identified early, helps ensure compliance with planning requirements and reduces the likelihood of unexpected costs later in the project.

What Is a Phase 1 Desk Study?

A Phase 1 Desk Study is the first stage of a site investigation and provides a Preliminary Risk Assessment for potential land contamination risks and environmental constraints affecting a development site. It is typically required to support a planning application and forms a key part of due diligence.

At this stage, the aim is to build a clear understanding of the site using existing information rather than intrusive works. This allows potential issues to be identified before committing to further investigation.

What does it include?

A Phase 1 Desk Study combines a desktop study, a site walkover survey and a structured risk assessment to establish the environmental setting and site history.

This typically involves reviewing historical mapping and historical land use, analysing aerial imagery and obtaining environmental data from sources such as the Environment Agency, the British Geological Survey and the local authority. Contaminated land registers and records of previous site activity are also considered, alongside a site walkover survey to identify visible constraints or evidence of contamination.

All of this information is brought together within a desk study report, supported by a conceptual site model. This model identifies potential contaminants, pathways and receptors, including risks to human health and controlled waters, and forms the basis of the Preliminary Risk Assessment.

How Much Does a Phase 1 Desk Study Cost in the UK?

The Phase 1 Desk Study costs UK developers typically encounter will vary depending on the size, complexity and history of the site.

In 2026, smaller and lower risk sites are often within the range of £600 to £1,500, whereas larger or more complex sites can exceed £3,000. The difference in cost reflects the level of detail required in the desk study and the amount of environmental data that must be reviewed.

Sites with a simple history and limited potential for contamination can usually be assessed more quickly. In contrast, sites with a history of industrial use or known land contamination risks require a more detailed assessment and a more comprehensive desk study report.

A Phase 1 Desk Study remains a cost effective starting point, as it allows risks to be identified early and can prevent unnecessary expenditure on intrusive site investigation where it is not required.

What affects the price?

The cost of a Phase 1 Desk Study is largely determined by how much information needs to be reviewed and how detailed the risk assessment needs to be.

Factors such as the size of the site, the complexity of historical uses and the availability of environmental data all influence the scope of the work. Where a site walkover survey is required, this will also affect cost, particularly on larger or more remote sites.

Additional inputs may be needed in some cases, for example a Coal Mining Risk Assessment from the Mining Remediation Authority, or further review of ground stability or flood risk data. Where the proposed development is sensitive, such as residential use, the level of assessment is typically more detailed to ensure that risks to human health are properly considered.

What Is a Phase 2 Site Investigation?

Where a Phase 1 Desk Study identifies potential risks that cannot be ruled out, a Phase 2 Site Investigation may be required. This stage involves intrusive investigation to obtain site specific data and confirm ground conditions.

Rather than relying on existing records, this stage focuses on direct testing of the ground. It allows potential land contamination, ground gas risks and other constraints to be confirmed or discounted based on physical evidence.

What Does a Phase 2 Investigation Include?

A Phase 2 Site Investigation typically involves a combination of boreholes, trial pits and sampling to obtain information about soil and groundwater conditions. Samples are sent for laboratory analysis, and where necessary, groundwater monitoring is carried out to understand groundwater sensitivity and behaviour.

At the same time, geotechnical information may be collected to assess ground stability and inform foundation design. The results provide site specific data that refines the conceptual site model and gives a clearer understanding of risks associated with the development.

Phase 2 Site Investigation Pricing in 2026

The cost of a Phase 2 Site Investigation depends on the extent of the work required and the level of uncertainty identified during the Phase 1 Desk Study.

For smaller residential sites, costs are often in the range of £2,000 to £6,000. Medium sized schemes may fall between £5,000 and £15,000, while large or complex sites can exceed £50,000 where extensive investigation is required.

Costs increase where deeper boreholes, additional sampling or extended monitoring are needed, particularly where risks such as ground gas or groundwater sensitivity are being assessed.

Ground Investigation Cost per Borehole

Drilling and sampling form a significant part of most intrusive investigations. In the UK, the cost per borehole typically ranges from £300 to £1,000, but can be significantly higher.

This variation depends on factors such as depth, access, ground conditions, the purpose of the investigation and the drilling methodology. Boreholes required to assess geological conditions or contamination at depth will generally be more expensive than shallow investigations.

Contaminated Land Assessment and Reporting

Following completion of a Phase 1 Desk Study and any intrusive investigation, the findings are brought together into a report that assesses land contamination risks and sets out recommendations.

This report explains whether contamination is present, what the risks mean in practical terms and whether remediation strategies are required before development can proceed. It also confirms whether the site is suitable for the proposed development.

Costs vary depending on site complexity, with lower risk sites typically requiring less detailed reporting, while more complex or heavily impacted sites require more extensive analysis and interpretation.

When Is Further Investigation Required?

Further investigation is only required where the Phase 1 Desk Study identifies potential risks that cannot be ruled out through a desktop study and site walkover survey alone.

If the Preliminary Risk Assessment demonstrates that the site is low risk and well understood, no additional work may be needed. Where uncertainty remains or an unacceptable risk is identified, intrusive investigation provides the detailed information required to support planning decisions.

Managing Site Investigation Costs

Keeping site investigation costs proportionate is largely a matter of sequencing and scope. Starting with a well prepared Phase 1 Desk Study ensures that the risk assessment is based on a clear understanding of the site.

Intrusive investigation should then be undertaken only where justified, and the scope should remain aligned with the proposed development. This approach avoids unnecessary work while ensuring that planning requirements are met and that risks are properly understood.

Why G&J Geoenvironmental?

When we work with clients, the aim is simple. We want you to understand exactly what your site is telling us so you can make informed decisions about your development.

Each Phase 1 Desk Study is prepared to provide a clear and realistic understanding of site conditions at an early stage. We combine environmental data, site history and site walkover survey observations to build an accurate picture of the development site.

Where further investigation is required, we design intrusive investigation works that are proportionate to the risks identified and directly relevant to the proposed development.

The outcome is a clear assessment of risks, a defined scope of any further work and a practical route forward for the project.

Summary

A structured approach to site investigation allows developers to understand potential risks at an early stage and plan accordingly. A Phase 1 Desk Study provides the initial assessment of land contamination risks, ground conditions and environmental constraints, while a Phase 2 Site Investigation is only required where those risks cannot be ruled out.

Costs will vary depending on site history, complexity and the level of detail required, but starting with a clear and proportionate assessment helps avoid unnecessary investigation and delays later in the project.

By combining a well prepared desk study, a realistic risk assessment and targeted intrusive investigation where needed, it is possible to meet planning requirements, manage costs and maintain progress on site.

Frequently Asked Questions

What is a Phase 1 Desk Study?

A phase 1 desk study is a preliminary risk assessment that reviews site history, environmental data and current conditions to identify potential land contamination risks and other environmental constraints affecting a development site.

How much does a geotechnical survey cost in the UK?

Costs vary depending on the scope of the investigation, but intrusive site investigations typically range from a few thousand pounds for small sites to significantly higher costs for large or complex developments.

What is a Phase 1 Contaminated Land Assessment?

A Phase 1 Contaminated Land Assessment is another term for a Phase 1 Desk Study and focuses on identifying potential contamination and assessing risks to human health and the environment.

When is further investigation required?

Further investigation is required where the Phase 1 Desk Study identifies potential risks that cannot be ruled out and additional site specific data is needed.

Do all sites require a phase 2 investigation?

No. If the Phase 1 Desk Study demonstrates that risks are low and well understood, further investigation is not required.