Geoenvironmental Consultants Ltd
Land Contamination Assessment & Risk Reports
The evaluation of contaminated land begins at the Phase I Desk Study stage (often referred to as a Preliminary Risk Assessment), which determines whether any potentially significant pollutant linkages are likely to be present in the surrounding area, including considerations for groundwater risk assessments. The subsequent Phase II Ground Investigation tests the significance of these pollutant linkages, initially through a Generic Quantitative Risk Assessment (GQRA) based on standard published assessment criteria.
​
A brownfield risk assessment is often necessary to comprehensively evaluate brownfield land contamination and its potential impact on the environment.
​
Where a GQRA identifies a potential risk or is insufficient to determine the significance of any risks, a site-specific Detailed Quantitative Risk Assessment (DQRA) can be carried out to more accurately quantify risks and ensure an appropriate response.
Introduction to Contaminated Land
Contaminated land refers to any area where harmful substances in, on, or under the ground could cause serious harm to human health and the environment. The Environmental Protection Act 1990 defines contaminated land as ground that contains substances that are or could be potentially hazardous to human health and the environment. A contaminated land risk assessment is an integrated analysis of a site to evaluate the degree of contamination present, identifying the contamination potential, the level of risk present contaminants, and whether actions are required to mitigate or remediate the hazard. This process is crucial in ensuring that land is safe for its intended use, whether it be for development, residential purposes, or other activities.
​
​
​
The first stage of contaminated land risk assessment is the Preliminary Risk Assessment, a qualitative assessment undertaken at the Phase I Desk Study stage. Quantitative contaminated land risk assessment is subsequently undertaken based on data acquired during the intrusive site investigation. and may take the form of a Generic Quantitative Risk Assessment (GQRA) or a Detailed Quantitative Risk Assessment (DQRA), depending on the site circumstances.
​
Understanding the impact of hazardous substances on ecological systems is crucial during these assessments.​
​
​
A contaminated land investigation is a thorough examination of a site to establish the properties and contamination characteristics of the land, including site reconnaissance. This investigation is designed to meet the objectives of BS 10175 “Code of Practice for the Investigation of Potentially Contaminated Sites” and follows the technical approach presented in Contaminated Land Report 11 “Model Procedures for the Management of Land Contamination” (Environment Agency). The investigation involves a tiered approach, assessing the risks from contaminated land to the environment and human health, and identifying potential contaminant linkages. The Environment Agency is responsible for regulating contaminated land site investigations, which are often required for brownfield sites and other areas with potential contamination.​
​
​
A conceptual site model (CSM) is a crucial component of a contaminated land risk assessment. It provides a visual representation of the site, including the source of contamination, the pathways through which contaminants can migrate, and the receptors that could be affected. The CSM is developed based on historical land use, environmental data, and site-specific information, and is used to identify potential risks and inform further investigation and remediation strategies. The initial conceptual site model is refined as more data becomes available, ensuring that the risk assessment is comprehensive and accurate.​
​
​
A GQRA uses conservative criteria (often published by regulatory bodies or other organisations) as an initial screen to identify contaminants that are of potential concern. For soils, these are contaminant concentrations (known as Generic Assessment Criteria (GAC)) that, if exceeded, may warrant further consideration or remediation. Collecting soil samples is crucial in this process to obtain chemical data on subsurface conditions. They are produced using an appropriate exposure model (in the UK, this is usually the Contaminated Land Exposure Assessment (CLEA) model), which requires a wide range of toxicity and exposure parameters to be input to allow calculation of the GAC.
​
Meeting planning conditions is essential in property development and regulatory requirements. Failure to satisfy these conditions can lead to the refusal of planning permission.
​
GACs are based on the ‘suitable for use’ principle and are available for several common land uses, such as residential, commercial, open space and allotments. The concentrations represented by the GAC are a function of the sensitivity of the site use, for example, the GAC for a residential land use are lower than for a commercial land use. The GACs used for contaminated land assessment in the UK are available from some sources, with the most commonly used being Category 4 Screening Levels (C4SLs) published by CL: AIRE on behalf of Defra in 2014, and Suitable 4 Use Levels (S4ULs) published by LQM/CIEH in 2015. Although developed using the same model, GACs published by different organisations can vary for the same substance due to the use of different input parameters. As such, the contaminated land assessor needs to be confident that the assumptions used in the development of the chosen GAC are appropriate for the subject site. However, all GACs are based on predominantly conservative assumptions (i.e. worst case) with regards to toxicity and exposure for each land use, and if simply used as thresholds for mitigation, can result in remediation works being undertaken that are not strictly necessary.
​
For waters, reference concentrations such as Drinking Water Standards (DWS) or freshwater Environmental Quality Standards (EQS) are often used as initial screening concentrations. However, these are not always directly applicable, especially when considering shallow groundwater quality and potential groundwater contamination.
​
​
​
A DQRA seeks to refine the assessment by taking site-specific data, such as soil parameters, building types, exposure durations, groundwater flow direction, distance to the receptor, etc, to determine Site Specific Assessment Criteria (SSAC). The DQRA may be relatively straightforward, using data that is readily available as part of the ground investigation, as well as any further information needed. In other cases, it may be necessary to undertake further targeted site investigation works to assess specific sources, pathways and receptors and build a more comprehensive dataset to feed into the model. As with all contaminated land assessments, the amount of information and level of detail required for the DQRA will depend on the assessment aims and objectives. If initial screenings indicate potential risks, further assessment may be required to ensure accurate results.
​
Human health risk assessment is a critical component in evaluating the concentration of contaminants in various media, such as soil, that may impact human health and necessitate ecological risk assessments. This assessment often begins with a risk screening process that identifies sites posing a low risk and progresses to more detailed assessments if generic criteria are exceeded, ultimately utilising specific tools developed by authorities to ensure safe exposure levels.
​
For soil contamination and the risks to human health, the CLEA model is usually the basis for calculating the SSAC and determining whether any potentially significant risks exist. The SSAC will essentially be used as a threshold, above which remediation works are likely to be required. This may simply involve comparing individual measured concentrations with the SSAC, but it is often more appropriate to calculate averages or mean values that are representative of a particular material or location, as this approach may be more consistent with the assumptions behind the SSAC calculation. Ultimately, this is a decision for an experienced contaminated land assessor who understands the rationale behind the model.
​
For groundwater, models such as ConSim or the Environment Agency’s Remedial Targets Methodology can be used to determine if recorded concentrations are likely to impact a sensitive receptor, such as a watercourse or a groundwater abstraction, or to calculate target concentrations which are unlikely to present a risk.
​
Assessments of the risks from ground gases are often complex and require consideration of many factors, although there are criteria published by organisations such as CIRIA and the BSI that can be used as an indication of a potential problem. The monitoring and assessment of ground gases is covered in more detail here.
​
​G&J’s qualified and experienced contaminated land assessors will determine the appropriate level of assessment to identify and quantify potential contamination risks and establish where remediation works are necessary to ensure a safe development. We aim to avoid unnecessary remediation works where this can be demonstrated through a high-quality risk assessment.
​
​
​
Human health risk assessments are a critical part of the contaminated land risk assessment process. These assessments involve comparing the concentrations of contaminants in media to which humans might be exposed to standards developed by authorities such as the Environment Agency and Defra. The contaminated land exposure assessment (CLEA) software tool is commonly used in the UK to undertake human health risk assessments. The risk assessment process considers the potential for contaminants to affect human health, including the risks associated with inhalation, ingestion, and skin contact. A detailed quantitative risk assessment (DQRA) may be necessary if generic assessment criteria are exceeded to determine whether the generic criteria are, in fact, overprotective.
​
​
​
Risk management and remediation are essential components of the contaminated land risk assessment process. Once a contaminated land risk assessment has been undertaken and unacceptable risks have been identified, remediation strategies can be developed to mitigate or remove these risks and ensure compliance with planning approvals. Remediation strategies may include the removal of contaminated soil, treatment of contaminated groundwater, or the installation of monitoring systems. The choice of remediation strategy depends on the type and extent of contamination, as well as the intended use of the land. A preliminary risk assessment report is used to inform the design of further contaminated land investigations, and a detailed quantitative risk assessment (DQRA) may be necessary to determine site-specific remedial targets. The Environment Agency and local authorities play a crucial role in regulating contaminated land remediation, ensuring that remediation strategies are effective and protect human health and the environment.
​
​
​
G&J’s qualified and experienced contaminated land assessors will determine the appropriate level of assessment to identify and quantify potential contamination risks and establish where remediation works are necessary to ensure compliance with the national planning policy framework and a safe development through our comprehensive contaminated land services. We aim to avoid unnecessary remediation works where this can be demonstrated through a high-quality risk assessment.
​
An intrusive investigation is a critical component of the assessment process that follows the identification of potential risks in Phase 1, often supported by reviewing historical maps.