The Brownfield Ground Risk Calculator

Brownfield land forms a significant land resource that is recognised by the UK Government as a key part of being able to achieve its housing targets and protecting green space.

"BGS award scoop for brownfield digital planning tool"

 Further information about the award 

Brownfield land forms a significant land resource that is recognised by the UK Government as a key part of being able to achieve its housing targets and protecting green space.

The Brownfield Ground Risk Calculator is a digital planning tool presented in a geographical information system (GIS). The Calculator has been developed by British Geological Survey (BGS) and its clients to understand and communicate the scale of risk and cost associated with brownfield ground conditions. The conditions considered are above and beyond those expected when normal development conditions prevail - these are often referred to as 'abnormals'. The ground conditions considered by the Calculator include: 1) soil and groundwater contamination; and 2) land stability and ground gases.

The likelihood of soil and groundwater contamination being present is influenced by the potential for past land uses to have resulted in pollution and for the underlying geology to allow pollutants to percolate through the ground. Examples of land uses highly likely to have resulted in contamination include chemical works, landfill sites and textile mills. Examples of land uses with a lower likelihood include offices and warehouses. We have evaluated potential sources of contaminants and different ways which they might move through the ground and reach sensitive receptors (people, surface water and groundwater). The presence of potential sources of contamination, pathways through which it moves and receptors were used to assign risk scores and along with information from Homes England to estimate remediation costs.

Land stability and ground gas hazards are influenced by hazardous natural and anthropogenic ground conditions. Examples of hazardous natural ground conditions include shrink swell clay and running sand. Examples of hazardous anthropogenic ground conditions include former coal mining areas and landfill sites. Land stability hazards were considered because of their potential to cause subsidence and damage properties. Ground gas hazards were considered because of the potential of gases such as methane and carbon dioxide to migrate into homes, presenting explosive and acute respiratory risks for people living there.

The Calculator is designed to inform decisions made early in the planning process by public bodies, developers and land owners. Decisions made early on in this process can affect the economic viability of building new homes on brownfield land, this includes any land that has a record of having been previously developed, including waste disposal or mineral extraction activities.

The Calculator produces Ground Risk Scores and Risk Mitigation Cost Estimates for both soil and groundwater contamination and geotechnical hazards. It is able to do this by using a variety of publicly accessible datasets.

The Calculator uses over thirty publicly available environmental datasets including those published by BGS, the Environment Agency and The Coal Authority.

Each brownfield site is divided into 50 x 50 m grid cells. The Calculator determines whether a risk is present or absent and assigns predetermined score to each grid cell. The scores were decided on using specialists in land contamination and engineering geology. The results are presented for each grid cell and at a site scale, each scale provides a summary of the risk score and cost estimate along with the datasets that were used in the calculation.

"BGS has worked with the GMCA to develop the Brownfield Ground Risk Calculator. The project has proved to be very useful and is contributing to the place based work to support delivery of housing and growth across Greater Manchester with its partners. The working relationship has been very good and BGS have worked hard to deliver a tool that helps GM partners make decisions on the development of brownfield land and sites across Greater Manchester." Murray Carr, Director of Land and Property, GMCA 

At a site level the Calculator shows to what degree potential development sites are expected to be affected by contamination or geotechnical hazards that affect building design and estimates costs to mitigate the risks.

Over 3000 brownfield sites across the GMCA area that are expected to be available and suitable for housing have been evaluated using the calculator.

USE CASE: The Environment Agency will use the Calculator to contribute to their understanding of the scale of regulatory effort that might be required by its staff for land contamination risk management by its officers over the next 5 years

Historical industrial processes often produced harmful by-products, residues and wastes that were poorly managed. The chemicals contained in these legacy materials can threaten human health and the environment. When developing post-industrial brownfield land, historic contamination often needs to be remediated to ensure the land will be safe, often at a significant cost to the developer or land owner.

USE CASE: Greater Manchester Combined Authority are using the Calculator in their Viability Assessment of the Greater Manchester Spatial Framework

Soil and groundwater risk mitigation cost estimates are presented in the Calculator. A closer look at brownfield sites in central Manchester shows that some land is likely to be more expensive per hectare to remediate than other areas.

"Working with BGS to develop a digital brownfield risk calculator will not only free up officer time for value adding activity a distilled version of the data will be made available through our open access Gateshead Site Information tool specifically for brownfield sites. The innovative approach of BGS together with the extensive local knowledge of our officers has produced a very robust a credible digital tool to support housing delivery." Neil Wilkinson, Spatial Planning and Environment Manager, Gateshead Council

Ground risk scores have been developed for all sites on the Gateshead Council Brownfield Register. The risk scores have been calculated for both geotechnical hazards and soil and groundwater contamination.

Ground conditions influence the design of new housing in two ways. Firstly, the ability of the ground to support the weight of the property without subsidence. Secondly, the building must form a safe barrier between substances present in the ground and the people living in it.

The hazards that can cause building subsidence or collapse and/ or result in the ingress of ground gas into a property that are evaluated by the Calculator include:

• current or former mining
• current or former landfill
• natural conditions affecting ground stability (e.g. landslides and compressible ground)
• naturally occurring radon

Geotechnical ground risk scores are presented in the Calculator. Large parts of Gateshead have been extensively mined for coal or used for waste management activities. The Calculator presents Ground Risk Scores for all of the sites on the Council's Brownfield Register. The results are presented in a web application hosted by ESRI ArcGIS Online.

USE CASE: Gateshead Council are using the Calculator to speed up planning consultation responses on land contamination risk management

Ground Risk Fact Sheets on issues of particular relevance in Gateshead have been produced for the end user. These include:

• coal mining and coal mining wastes
• landfill
• galligu (waste product from the chemical industry)
• dioxins
• asbestos

The issues affecting Gateshead are also present in other parts of the UK meaning the fact sheets may also be useful in other areas.

The Calculator is currently being used as an internal digital planning tool by Gateshead Council. A new version will soon be published for developers and other external stakeholders who might benefit from a better understanding of ground conditions for brownfield land in Gateshead. This will form part of an exciting new online initiative by the Council called the Gateshead Site Information Tool.

Please get in touch with the BGS if you feel something similar to the work described would be of benefit to your organisation. We are really keen to enhance the contribution that data, geoscience and visualisation can have on the effective utilisation of brownfield land.

For an informal chat please contact  Dr. Darren Beriro , darrenb@bgs.ac.uk.