Land Contamination Assessment

Contaminated Land Assessments

Contaminated land risk assessment is a structured environmental investigation that establishes whether a development site is affected by harmful substances in the soil or groundwater, and if so, what risk those substances pose to human health, controlled waters and the wider environment.

It is the process through which a developer demonstrates to a local authority that potentially contaminated land is suitable for its proposed use, or identifies the remediation needed to make it so to comply with the concept of sustainable development.

For brownfield land, former industrial land and any site with a history of activity that could have left contamination behind, a land contamination assessment is one of the most common risk assessments required to support a planning application.

Without it, a local authority cannot be satisfied that the proposed development is safe and poses no risks to health and the environment, and the application is likely to be delayed, queried or refused. 

What Counts as Contaminated Land? 

Ground contamination arises where hazardous substances are present in, on or under the ground at concentrations that pose a risk to people, property or the environment.

The potentially hazardous substances most commonly encountered during a land contamination survey include heavy metals such as lead, arsenic and cadmium, hydrocarbons from fuel and oil spills, asbestos fibres in soil or made ground, radioactive substances, volatile organic compounds, solvents, ground gases such as methane and carbon dioxide, and residues from past industrial processes including tanning, metalworking, chemical manufacture and waste disposal.

Land does not need to have an obvious or visible history of pollution to be affected. Many sites that appear unremarkable on the surface carry a legacy of contamination from activities that took place decades earlier, particularly where former uses included petrol stations, gasworks, scrapyards, dry cleaners, landfill sites, railway sidings or any form of heavy industry.

As well as residues from a site’s previous industrial use, invasive plants such as Japanese knotweed can also contaminate land.

Environmental Risks

The presence of contamination is assessed not just by the existence of a hazardous substance, but by whether a viable pathway exists for that substance to reach a receptor: a person, a watercourse, a building or an ecosystem.

This source-pathway-receptor relationship, known as a pollutant linkage, is the central concept underpinning how contamination risk is assessed in UK environmental and planning law.

The statutory definition of contaminated land is set out in Part 2a of the Environmental Protection Act 1990, inserted by the Environment Act 1995 and in force in England since April 2000.

Under this regime, land is formally classified as contaminated where it meets specific risk-based criteria relating to harm to human health, harm to protected ecological sites, or pollution of controlled waters.

Local planning authorities have a statutory duty to inspect their areas and identify land that meets this definition.

In practice, most contamination encountered during the development process is dealt with through the planning system rather than through formal Part iia determination, but the same underlying risk principles apply.

Human Health Risk Assessment

The generic quantitative risk assessment investigates the risk of significant harm to site users through a human health risk assessment. This looks specifically at water supplies on the site and surrounding area.

Land Contamination Issues and Planning

The National Planning Policy Framework (NPPF) places clear expectations on developers and landowners when it comes to previously used land and contaminated areas.

Paragraph 197 of the NPPF states that responsibility for securing a safe development rests with the developer and the landowner.

Paragraph 196 sets out the criteria that planning decisions should ensure are met: that the site is suitable for its proposed use taking account of ground conditions and any risks arising from contamination or land instability; that after remediation, land should not be capable of being determined as contaminated land under Part iia of the Environmental Protection Act 1990; and that adequate site investigation information, prepared by a competent person, is available to inform these assessments.

In practical terms, this means that for any development on a site with a history of potentially contaminative use, the local planning authority will expect a land contamination assessment to be submitted as part of the application, or will impose a planning condition requiring one to be carried out before construction begins.

Qualitative Assessment

Where contamination is identified, the local authority will require a remediation strategy and verification that the remediation has been completed satisfactorily before the development is occupied.

Building Regulations also impose separate requirements, requiring that reasonable precautions are taken to avoid risks to health and safety arising from contaminants in the ground beneath a building.

Where contaminated soil is to be moved or treated as part of a development, the soil may be classified as waste under the Environmental Permitting Regulations, requiring an environmental permit from the Environment Agency (EA) before treatment or relocation can take place.

Failing to consider these requirements early in a project can become a significant cost to the developer and lead to programme implications.

Assessing Land Contamination and Site Conditions

Contaminated land investigation assessments follow a staged, internationally recognised methodology, with each stage building on the findings of the one before it.

Generic quantitative risk assessment criteria are applied, followed by site-specific assessment criteria.

Not every site will require every stage: the process is designed to be proportionate, moving to more detailed investigation only where the evidence of past activities indicates it is necessary.

Phase 1: Preliminary Risk Assessment

The first stage is a non-intrusive desk-based study, often referred to as a Phase 1 assessment.

This involves researching the historical uses of the site and surrounding area through reviewing historical maps, aerial photographs, trade directories and planning records, alongside a review of environmental databases covering landfill sites, pollution incidents, licensed waste facilities and groundwater vulnerability.

A site walkover is carried out to observe current conditions on the site and surrounding land, identify visual or olfactory evidence of contamination, and note any features such as surface water, fuel storage, hardstanding, drainage and signs of made ground.

The findings of the desk study and walkover are brought together to develop an initial Conceptual Site Model, a technical approach that identifies potential sources of contamination, potential contaminant linkages and the receptors that could be affected.

The Phase 1 contaminated land investigation concludes by categorising the level of environmental risks the site presents and determining whether more detailed investigation is warranted to provide further information.

Phase 2: Intrusive Site Investigation

Where the Phase 1 assessment indicates a potential risk, a Phase 2 intrusive investigation is carried out to gather direct physical evidence of site conditions, ground contamination or contaminant sources.

Site reconnaissance typically involves digging trial pits or drilling boreholes to collect soil samples from various depths and locations across the site, installing groundwater and ground gas monitoring wells where relevant to assess the water environment and groundwater contamination, and sending samples to an accredited laboratory for chemical analysis.

The laboratory results are compared against published assessment criteria to determine whether contaminant concentrations exceed levels considered acceptable for the proposed end use of the site.

Geotechnical testing is often carried out alongside the chemical analysis, assessing soil stability, compaction and bearing capacity to determine the ground’s suitability for the proposed construction.

The Phase 2 investigation refines the Conceptual Site Model with empirical data and establishes whether remediation will be required and, if so, the likely scale and nature of the work that may be required.

Phase 3: Remedial Targets Methodology and Verification

Where significant quantities of contamination requiring remediation are confirmed, a Phase 3 remediation strategy sets out the specific measures that will be used to address adversely affected areas.

This may involve a tiered approach: remedial targets methodology may include excavation and removal of potentially hazardous or contaminated material to ensure no new pathways for contamination are created, soil treatment or stabilisation, capping with clean material, vapour barriers, or long-term monitoring of ground gas or groundwater.

Following the completion of remediation works, a verification report is produced to confirm that the agreed remediation has been carried out successfully and that the site now meets the standards required for its intended use.

This verification report is typically required to discharge the relevant planning condition before the development can be occupied.

When is a Land Contamination Risk Assessment Required?

Investigation of contaminated areas is likely to be required in several circumstances. Where a local authority is determining a planning application for new development on a site with a history of potentially contaminative use, a desk-based assessment will usually be requested at minimum.

For brownfield sites (previously developed land) a more detailed assessment is the norm, given the higher statistical likelihood of historical contamination than greenfield sites.

Property transactions involving land with an uncertain or industrial history often call for an assessment as part of buyer or lender due diligence, particularly where the National House Building Council or a mortgage lender requires confirmation that contamination risks have been properly investigated.

A change of use application, for example converting commercial or industrial land to residential use, will typically trigger a more rigorous assessment given the increased sensitivity of residential occupants as receptors.

Where evidence of contamination, such as discoloured soil, odours, buried tanks, hardstanding inconsistent with current use, or known historical industrial activity, is identified by risk assessors during any stage of site assessment, further investigation will be required regardless of the development type.

Reading a Contaminated Land Report

A contaminated land report produced following a land contamination survey will typically include a summary of the site’s history and current condition, the results of the desk study and Conceptual Site Model, the findings of any intrusive investigation including laboratory analysis results, an assessment of the risk posed by any contamination identified, and recommendations either confirming the site is suitable for its proposed use or setting out the remediation required.

Where remediation is recommended, the report will outline the proposed method, the anticipated cost and programme implications and the verification process that will be used to confirm the work has been completed to the required standard.

The report should be prepared by a competent person, in line with the requirements of the NPPF, and should be capable of being submitted directly to the local authority and, where relevant, the EA to discharge any associated planning conditions.

Booking a Land Contamination Assessment

If you are dealing with contaminated land issues, the right time to commission a land contamination survey is as early as possible in the development process, ideally before a site is acquired, or at the earliest opportunity once acquisition is agreed.

Identifying contamination risk on land affected early allows it to be factored into the site appraisal, the development viability assessment and the design of the scheme, rather than it leading to costly delays and potential liabilities once the project is already underway.

A land contamination assessment should be carried out by a qualified geo-environmental consultant with relevant experience of the type of site and former land use involved. The consultant should be familiar with the requirements of the relevant local authority and the Environment Agency, and should hold appropriate professional accreditation.

Satisfy Legal Obligations with Site Specific Information

Whether you are a developer, housing provider or landowner, we can connect you with experienced geo-environmental consultants who can carry out land contamination surveys and produce the relevant information needed to satisfy local planning authorities and the EA across the UK.

Use our free service to get fast, no-obligation quotes from trusted geo-environmental consultants in our network.

Fill in the form at the top of this page, and we will connect you with a specialist who can carry out your land contamination assessment, advise on the right level of investigation for your site to ensure that you comply with regulatory requirements and provide confidence as you progress your planning application.