What Is A Phase 1 Contaminated Land Desk Study, And Why Do You Need One?

Key Takeaways

• A Phase 1 Desk Study evaluates contamination risks, assesses land suitability for development and offers a Preliminary Risk Assessment based on historical data and environmental conditions.

• Key components of the study include a geo-environmental and geotechnical evaluation, and the development of a Conceptual Site Model to identify potential pollution linkages.

• The findings are detailed in a comprehensive report that informs the design of subsequent investigation and remediation works, assists with decision-making for developers and planners, and ensures compliance with regulatory requirements.

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Understanding Phase 1 Contaminated Land Desk Studies

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A Phase 1 Desk Study serves as an initial evaluation with the following purposes:

• Identify potential pollutant linkages and develop an initial Conceptual Site Model (CSM).

• Qualitatively assess potential risks to determine the likelihood of potential pollution linkages being significant, known as a Preliminary Risk Assessment

• Determine the scope of subsequent investigation works required to assess the significance of the identified potential pollutant linkages.

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In essence, a Phase 1 Desk Study identifies the likely sources of contamination, the environmental setting of the site and the potential receptors (those exposed to the contamination sources). This approach allows early identification of potential risks and provides the basis for subsequent stages of investigation.

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Typically, a Phase 1 Desk Study can be completed in about one week, depending on the complexity of the site. The study involves:

• Compiling historical land use data

• Assessing information related to the geology, hydrogeology and hydrology of a site

• Reviewing information datasets from authoritative sources such as the Environment Agency, Local Authority, Mining Remediation Authority, British Geological Survey and more.

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The output of the desk study is Preliminary Risk Assessment that offers a clear summary of the findings to allow developers and planners to make informed decisions about the site risks, development potential, investigation requirements and possible remediation measures.

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Qualified and experienced consultants and engineers are key to producing robust assessments and ensuring that sufficient and relevant data is collected

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Key Components of a Phase 1 Desk Study

A Phase 1 Desk Study is the foundation for the identification of potential pollutant linkages and understanding the environmental risks of a site. A robust Desk Study and Preliminary Risk Assessment can enhance the value of a property by providing clarity regarding its likely suitability for development.

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As well as contamination risks, the desk study may include a preliminary evaluation to identify geological constraints that could impact development, based on analysing historical, geological, and environmental data relevant to the site.

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A walkover survey is an important element of most desk studies which allows an assessment of potential contamination sources and risks based on the current site use and setting, and facilitates an inspection of potential geohazards and environmental issues that may not be evident from desk-based research alone. The walkover findings are combined with the desk based research to allow a comprehensive understanding of the condition of the site.

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Site History and Environmental Context

Understanding the site history and environmental context of a site is the basis of a Phase 1 Desk Study. This requires a thorough review the historical site use to identify any previous contamination hazards that may not be apparent from contemporary records or a site walkover survey. For example, historical maps might reveal previous uses and features such as tanneries, gasworks, ground disturbance, tanks and mineshafts, which increase the potential for contamination or ground stability risks.

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Analysing historical data such as maps, photographs and other records helps:

• Identify the likely pollutants affecting the site

• Pinpoint the locations of potential contamination sources

• Understand the historical development of the site and any past incidents that may have occurred related to contamination or ground instability

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Analysis of historical information to identify past site activities provides valuable information relating to site uses and features for which no obvious above ground evidence may remain on the site, but which may have been the source of contamination which is still present beneath the surface. For instance, past mining activity and industrial uses, such as long gone gasworks, may present environmental hazards despite no current evidence remaining of these past industrial uses.

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Data on past contamination events can also assist in assessing current risks. Records of more recent environmental incidents, such as spills and other pollution incidents, are readily available, while past press reports may provide information relating to older and / or more significant incidents, such as major contaminant spills, mine gas explosions and other incidents that have resulted in damage or injury.

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A Phase 1 Desk Study compiles all the available historical and environmental data to develop a comprehensive understanding of the likely condition of the site, identify potential contamination risks and inform the development of a Conceptual Site Model.

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Regulatory Compliance and Planning Information

Regulatory compliance is an important consideration for a Phase 1 Desk Study, particularly on sensitive sites. Reports should be completed in accordance with any requirements of local authorities and environmental agencies, which may require consultation to ensure all necessary elements are covered.

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Various guidance is available on how to produce a Phase 1 Desk Study and Preliminary Risk Assessment, including the overarching Land Contamination: Risk Management (LCRM) framework produced by The Environment Agency, and plays a key role in defining standards for contaminated land assessments.

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Completion of a Phase 1 Desk Study is commonly mandated by planning consents as a pre-commencement condition to ensure development safety. A Preliminary Risk Assessment is usually the minimum that must be submitted and approved by the Local Planning Authority prior to development, to demonstrate potential risks have been identified and that development can safely proceed.

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Surrounding Land Use Analysis

It is not just the current and historical on-site uses that have an influence of the level of contamination risk. Assessing the land use of the surrounding area is also an important element of a Phase 1 Desk Study. As well as potential contamination sources, neighbouring land uses may represent sensitive receptors for on-site contamination.

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The potential impact of surrounding land uses will be significantly influenced by the underlying geological and hydrogeological conditions. Often the highest risk off-site land uses are those such as waste management sites / landfills and mine workings, which may be a source of ground gases that can migrate through the ground beneath the site.

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Neighbouring industrial sites and fuel stations may represent a risk where contamination from leaks and spills can migrate onto the site vis groundwater in a contamination 'plume'. More generally, significant nearby industrial activity and urbanisation can result in contamination via the atmospheric deposition of pollutants emitted to air, such as lead which was once a common component of vehicle exhausts and industrial emissions.

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Developing a Conceptual Site Model (CSM)

Developing a Conceptual Site Model (CSM) is an important output of the desk study which summarises the potential pollutant linkages and risks.

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A Preliminary Risk Assessment includes developing an initial CSM as a foundational element. Key points about the CSM are:

• It should be created early in the investigation

• It is refined as more data becomes available

• It helps identify potential data gaps

• It guides hypothesis formulation for further investigation

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The source-pathway-receptor approach (S-P-R) is the basis for understanding relationships in Conceptual Site Models. It helps identify the links between potential contamination sources, the receptors which may be exposed to the contamination sources, and the exposure pathways which may connect the sources and receptors.

 

As the assessment progresses beyond the desk study phase, the CSM should be refined and updated to reflect the latest findings.

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The Role of Site Walkovers

A site walkover survey gathers information that desk based research alone may miss. It also allows the assessment of site constraints that may influence the selection of suitable methodologies for subsequent site investigation works.

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During a site walkover, engineers record the presence and condition of structures, the presence of potential contamination sources such as tanks, evidence of contamination such as staining, odours and distressed vegetation, as well as other issues such as invasive plant species like Japanese Knotweed.

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A thorough site walkover identifies signs of ground contamination not visible through desk study alone, ensuring all potential issues are addressed early in the development process.

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Potential Contamination Risks and Further Investigations

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