Why Do We Conduct Phase 1 Desk Top Studies?

What is a Phase 1 Desk Top Study?

A Phase 1 Desk Top Study (or Phase I DTS) is a review of all available published information relating to a site’s historical, environmental, and geological setting. The purpose of this review is to determine an initial risk rating to plan the following stages of investigation. This is done by identifying any potential ground or environmental related hazards that can pose a potential risk to human health and controlled waters.

Carrying out these studies often saves time and money by identifying potential contamination risks at an early stage, which helps to quickly establish how to proceed with any site investigation, or whether a site investigation is not required.

When is a Phase 1 DTS needed?

A Phase 1 Desk Top Study should be undertaken at the start of the process of site assessment and  should provide a summary of the site settings through a site walkover and data review. This leads through to the production of a Conceptual Site Model (CSM), where if potentially active pollution pathways are identified will shape any subsequent Phase 2 intrusive ground  investigation.

Phase 1 Desk Top Studies are generally required by the Local Planning Authority as part of the regulatory requirements of planning departments, National Home Building Council (NHBC) and the Environment Agency.

What’s included in a Phase 1 Desk Top Study?

Phase 1 Desk Top Studies generally consist of the following:

Review of site settings including:

  • Current and Historical Industrial Land Use that are pertinent to the site development. This should identify any potential sources of contamination that can have a potential risk to future site users and involves review of historical mapping dating back to the late 1800’s and a physical site walkover.
  • Desk based assessment of Waste Sites and Landfill records– this includes any pollution incidents, waste exemption etc.
  • Hydrogeology – This includes the presence of Aquifers in both superficial and bedrock deposits as well as groundwater vulnerability and, surface and groundwater abstractions.
  • River and Coastal Flooding – Includes the Risk of Flooding from Rivers and Sea (RoFRaS), Historical events and flood zones.
  • Geology – includes Made Ground, Superficial and bedrock Geology.
  • Natural Ground Subsidence – Shrink swell clays, Running Sands, Compressible and Collapsible Deposits, and Landslides.
  • Mining, ground workings and natural cavities – Mining is much more of a risk in the northern counties and thus contact with the Coal Authority may be needed.

Benefits of a Phase 1 DTS

  • Phase 1 DTS provides an insight into possible environmental and geotechnical concerns that may have been identified by the preliminary conceptual site model.
  • It means that any risks identified can be specifically targeted during an intrusive investigation and to assess the implications any potential aspects may have on land liabilities and value as part of a property transaction.
  • In some cases, it is possible to remove the need for an intrusive investigation if there is an absence of any potential risks however this is ultimately decided by the Local Planning Authority.

What about after a Phase 1 DTS?

In most cases, if a Phase 1 Desk Top Study has been requested by a Planning Condition this is because the regulator hold information on the general area such that it is often the case that a Phase 2 site investigation will be required. The Phase 2 investigation follows a Phase 1 Desk Top Study in order to consider potential risks to future site users that have been identified in the CSM in relation to  source, pathways, and receptors. These site investigations can also be requested for geotechnical assessment to aid in proposed design works and it is cost effective to combine both geotechnical and environmental aspects.

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Hannah Spurling 

Geo-Environmental Consultant