Phase 1 Desk Studies
What Is a Phase 1 Desk Study?
Phase 1 Desk Studies can be Contamination or Geotech specific. They can also be combined as a Geo-Environmental Study.
Guidance for undertaking Desk Studies is provided by British Standard BS5930:2015 and BS10175:2013. The first stage of a Contamination or Geotechnical Investigation should always be a desk study (sometimes known as a ‘Phase One’ or ‘Desk Top Study’). This will provide information on the historical, environmental, geological, hydrogeological and hydrological site setting in order to establish likely contamination and geotechnical ground related risks for a site.
What Is Involved in a Phase 1 Desk Study?
A Phase 1 Desk Study is a preliminary risk assessment for the collation and review of relevant information regarding the historical, geological and environmental data of a site. It is used to ensure proper planning of subsequent stages of a site investigation and development of a site.
The Phase 1 Desk Study will aim to identify any potential ground related hazards or contamination sources. It will also look at pathways and receptors which could pose a risk to human health, vegetation, wildlife, controlled water structures or associated services.
Investigations begin by looking at historical maps of the site and area and gathering environmental information. This type of information includes the former use of a site. Sites of interest would include historical landfills, factories, industrial land, manufacturing depots and agricultural land.
Geological, hydrogeological and hydrological information is reviewed, such as rock type, aquifer designations, local water courses and flood susceptibility.
For contamination desk studies, an initial site inspection is made to visually evaluate the site then a risk assessment will be produced. This will consider:
- Sources of contamination
- Pathways (contamination transfer)
- Receptors (including current and future users of the site, plants, groundwater and surface water)
Sources of contamination which can be present include historical pesticide usage (such as lead and arsenic found in dusting powders used in orchards), animal burials and backfilled ponds. Historic clay pits and quarries that have been infilled may also be a source. These often host a variety of contaminants including asbestos and can also potentially be a source of ground gas. Ground gases include methane and carbon dioxide, which primarily come from landfill or historical landfill sites.
Once this process is complete a conceptual site model is produced which indicates a risk for each receptor from the contamination sources identified at the site. Depending on the levels of risk identified, further investigations may need to be undertaken.
What Does it Look At?
The Phase 1 Desk Study will normally include:
- Reviewing historical OS map data;
- Purchasing of a Landmark Envirocheck / Mining and Ground Stability report;
- Reviewing of online databases including British Geological Survey, Environment Agency, Radon, MAGIC and UXO;
- Production of preliminary conceptual site models;
- Producing preliminary assessments of contamination and geotechnical related risks; and
- Providing recommendations for intrusive investigations, where required.
What Is the Difference Between a Greenfield and Brownfield Site?
Greenfield sites are predominately undeveloped land either in a city or rural area. This land is likely to have been used for agricultural purposes historically. It can also be undeveloped land in a city or suburban area.
Brownfield sites are sites which have been used before for development. They are commonly disused or derelict prior to the application for redevelopment and often have been used previously for industrial and commercial purposes. Brownfield sites often have more significant contamination issues associated with them due to historical usage, however this is not always the case.
When is a Phase 1 Desktop Study Required?
It is recommended that before buying a site or property, a desktop study evaluating any associated risks with the site and subsequent liabilities to the purchaser are identified.
A Phase 1 Desk Study will often be required as part of planning conditions set out by your Local Authority. A Desk Study is required to satisfy various regulatory requirements as designated by Planning Departments, Environmental Health, The Environment Agency, Building Control or the National House Building Council (NHBC).
What is Included in a Phase 1 Desktop Report?
EMS Geotech’s Phase 1 Desktop Reports will include as a minimum:
An Executive Summary- summarising the findings of the report
All Relevant Site Details- to include site name, boundaries, usage, proposed usage & details of the walkover survey
Historical Appraisal – a review of historical site usage based on past structures, ordanance information and the surrounding area
Geological Appraisal – This may include factors such as artificial ground, superficial strata, bedrock, mining, geomorphology, natural ground subsidence etc
Environmental Appraisal – This will include aspects such as flooding, hydrology, pollution history, landfill use, contamination sources and hydrogeology
Conceptual Ground Model – This a preliminary risk assessment of potential ground related hazards and potential contamination sources. It also looks at their pathways and receptors where there could be potential risks to human health and other factors.
Site Investigation – any recommendations if required. These could include a Phase 2 Intrusive Investigation, Ground Gas Monitoring, Flood Risk or Contamination Investigation etc
What Are the Limitations of a Phase 1 Desk Study?
There are limitations of a Phase 1 Desk Study in that it is a desk-based report, based on an evaluation of risks associated with the site through analysis of available site information. The findings are not based on any intrusive ground investigations and subsequent findings. Occasionally, due to this, there may be other additional ground related hazards or contamination which is not able to be identified through the Phase 1 Desk Study alone.
What Do I do After the Phase 1 Desk Study is Complete?
If the Desk Top Study has been commissioned to satisfy planning conditions, your completed report must be submitted to your Local Authority Planning Department.
If the report has identified further investigations, for example a Phase 2 Site Investigation, EMS Geotech will be able to guide you through the process and undertake this on your behalf. More information regarding Phase 2 Site Investigations can be found here
If timescales are tight, and subsequent remedial action is thought to be likely, a Phase 1 Desk Study and a Phase 2 Site Investigation can be undertaken simultaneously.