“The nation that destroys its soil destroys itself” President Franklin D Roosevelt, February 1937.
Humans have relied on soil for millennia but, globally, soil health is threatened, particularly by climate change and intensive agriculture. The past decade has seen increased policy focus on soil, as the impacts of soil degradation on carbon stocks and the wider ecosystem have come under scrutiny. Government policies across the world are now starting to reflect the need for soil protection. However, effectively implementing such policies within the construction sector will require a significant cultural shift. Best-practice soil management and reuse, and the use of reconstructed soil, can contribute to a solution that improves soil health and quality and plays a role in mitigating climate change. Global targets for soil health, quality and its carbon stores must also be part of any serious efforts to reverse its decline.
Context & Issue
Soil consists of minerals, organic matter (specifically the material left over from decomposing plants and animals), organisms, water and gases. It underpins the food system, contains nutrients needed for plants to grow, and stores water. It supports biodiverse habitats; one gram of soil contains tens of thousands of microbial species. Soil acts as a filter for water, so it enters rivers more purified, and plays a key role in flood management, holding water after heavy rainfall. It provides a platform to allow construction. It also offers the most significant carbon storage system on earth, helping to regulate the climate.
Despite its life-giving properties, soil is in crisis across the world. Along with the effects of intensive agriculture, a growing population has caused significant changes to land use and contamination of soil. It is claimed that 3 cm of topsoil is generated every 1,000 years (UN FAO, 2019), yet in England and Wales roughly 2.9 million tonnes of topsoil are eroded annually. Most soil in England is classed as either ‘degraded’ or ‘very degraded’ (Environment Agency, 2019). Once soil becomes degraded, it can potentially emit greenhouses gases: carbon dioxide, methane and nitrous oxide.
On construction projects, the enthusiasm for projects to begin can be at the expense of highest quality, planned soil management. The tendency to strip sites and stockpile soil remains common; reuse is frequently an afterthought. Planning early to understand soil resources on construction sites (a Soil Resource Plan with Survey) and prepare for their reuse is too often overlooked. This creates the conditions for damaging soil and the risk of it being a waste material. Many consultants and advisors are pushing hard to change this behaviour and to create more educated clients.
Soil on construction sites are at risk of compaction as well as poor stockpiling conditions. Heavy machinery use increases soil compaction, compressing the soil structure and reducing porosity, nutrient cycling and gas exchanges, limiting productivity.
The risk of damage is increased for heavy clay soil during wet periods. More frequent, erratic weather patterns could increase this risk if it becomes more challenging to follow handling and management procedures on-site.
Another challenge is to encourage people’s engagement and understanding of soil, at individual, professional, societal and political levels. There is a clear need for political leadership and commitment to managing and improving soil health and quality. This will ensure its role in mitigating climate change is protected with waste creation and disposal minimised.
Addressing the issue
The UK is at a crossroads in deciding how it approaches soil management. Currently, soil accounts for the greatest tonnage of waste disposed to landfill in the UK. The complexity and relatively low environmental priority of soil creates significant challenges to its future management but, already, there is a lot of knowledge and expertise available to address the issue. The UK Government’s Soil Health Action Plan for England intends to address the challenge of increasing soil degradation by supporting the 25-year Environment Plan’s ambition for sustainable soil management by 2030. The scale of this crisis is finally appearing high on international political agendas too.
Industry can be empowered to take ownership of the issue and develop solutions for better soil management. The CL:AIRE Definition of Waste: Development Industry Code of Practice (DoW CoP) was the first, and remains a flagship initiative for the construction industry. It works within the principles set out in the Department of Business Innovation and Skills ‘Regulators’ Code’ (Office for Product Safety and Standards, Regulators’ Code) and remains a joint industry – regulator approach to soil management. A key objective of its design was to support the regulators by creating a system which clearly identifies low risk projects and activities, thus allowing them to focus resources on the opposite. Since its launch in 2008, the DoW CoP has allowed the sustainable reuse of over 160,000,000 m3 of soil and excavated materials, either on the site from which they were excavated, or on an alternative receiver site.
Landfill and soil waste
More needs to be done in the UK to discourage soil ending up in landfill. Defra’s 2022 statistics on waste (Defra, 2022) show that 58% of landfill tonnage is soil, most of which was removed for civil engineering projects and housebuilding. The situation is deeply ironic: removing and separating the soil from its natural environment means that it is effectively ‘lost’, yet this also leaves the problem of having to dispose of the removed soil, coupled with a need for importing virgin materials to make up the shortfall. The extraction and use of these replacement materials come with their own list of negative environmental, social and economic issues. The UK urgently needs a policy and regulatory system to stop this huge amount of soil going to landfill, whilst ensuring soil can be reused to a demonstrably high standard of environmental protection. In laudably chasing waste minimisation, care is needed to avoid creating the conditions for a race-to-the-bottom with regards to operational standards.
There are potential risks associated with soil when it is displaced, whether by industrial extraction processes and landfilling, or through erosion and climate pressures. The current Waste Strategy for England (Defra and Environment Agency, 2018) ignores the loss of soil to landfills despite these two issues being connected. This needs to be addressed. Such quantities of soil ending up in landfill sites is an indication of the low interest value accorded to the soil by UK citizens, society, politicians and policy makers. The two greatest inhibitors to soil reuse (and diversion from landfill) as they make it simply impossible are
- a lack of local potential receiver sites (e.g. a site with a requirement for soil), and
- non-alignment of donor (e.g. a site with surplus soil) and receiver sites during construction phases.
Where soil has been stockpiled, in the hope of eventual reuse, they readily become a burden to the holder. This increases the likelihood of them becoming a waste, (e.g. the likelihood of discard is increased) and certainly degrades their value ( by virtue of being a waste rather than a resource) to the point where they become benchmarked against some of the lowest grade waste streams we manage as a society. For example, Letsrecycle.com shows the market prices for many recycled materials. Negative values are only really associated with, unsurprisingly, the lowest quality materials such as Mixed Recycling facility films (plastic bags and wrappings), glass and low grade wood. That soil is frequently valued as poorly as such low grade wastes demonstrates how far the construction sector needs to change its behaviour if it is to truly value soil as a natural resource.
Creating the conditions for industry to set up high-quality, fixed soil treatment facilities, which can hold these valuable materials until the receiver site (that which is accepting soil) is identified and ready, would certainly play a huge role in addressing this negative situation. Poor performing treatment facility operators must not be allowed to unlevel the playing field against operators charging for a quality service to manage a valuable resource. The concept of ‘geo-resource’ hubs has also been developed by colleagues at the University of Plymouth, which captures the concept well.
Conversely there has been a tendency to overlook the benefits of bringing displaced soil back into its own environment. These benefits are detailed below.
When soil is damaged, it cannot perform the essential task of storing carbon. Greenhouse gases are emitted in greater amounts. Lateral diffusion transfers nutrients to water and leads to degradation of aquatic ecosystems, placing an even greater strain on the environment.
Best-practice soil management helps address these issues and improves soil functionality at completed sites, beginning the process of re-capturing carbon back into the soil.
Uncompacted soil allow water to infiltrate, reducing surface runoff and the leaching of nutrients into water bodies during wet weather. Soil also retains water for plants to access during drier periods and this retention ability is essential for the creation of a healthy sub-soil ecosystem. Soil that has been sealed cannot hold rainwater. Replacing open areas and covering soil with a hard surface such as concrete (soil sealing) can have a significant negative impact on the above processes. Over a large area it becomes especially problematic. This flags how imperative it is to consider this issue at the early site project design stages as part of a soil resource plan.
Biodiversity net gain
A healthy local habitat is dependent on the quality of the soil underpinning it. Our understanding of the importance of sub-surface interactions has increased dramatically. We appreciate more than ever the vital role that mycorrhizal fungi and bacteria play in creating optimum growing conditions. Where soil is damaged, either physically or biologically, it follows that this will be reflected negatively on the surface. This ultimately hinders any effort to improve biodiversity of construction sites.
Lost soil can be reconstructed. This could reduce the pressure on valuable and finite topsoil and support both sustainable development and food security. Inert materials (a frequent waste stream of construction operations) can be carefully mixed together to create a substrate with the characteristics of a healthy soil. This can be used in the manufacture of topsoil for urban grasslands, and potentially in the future for materials in high-value markets, such as horticulture and agriculture.
Cornwall’s Eden Project is an impressive example of infrastructure built using reconstructed soil in 8 hectares of a former sand quarry. Here, more than 80,000 tonnes of reconstructed soil were made by mixing locally-sourced, readily available waste materials. The resultant soil has a much higher organic component than most natural soil and has provided an excellent laboratory to assess the potential of reconstructed soil and how it might be optimised for widespread use. The team at the University of Plymouth has produced soil from suitable waste materials, working to improve their efficiency and nutrient retention, and influence both their deployment and the regulations surrounding their use. This work hopes to demonstrate the potential of reconstructed soil from waste as a viable option for communities across the world who need to rebuild their soil resources. This work continues under the ReCon Soil project, more details of which can be found at https://www.claire.co.uk/projects-and-initiatives/dow-cop
The components of natural soil can be varied but it is possible to develop reconstructed soil that potentially function better than natural soil. There is an obvious link here to material reuse, the circular economy and carbon capture.
Another benefit of soil creation is that it can be made to a specification. Depending on the application, the health of reconstructed soil needs to be assessed for its suitability, based on its end use location. A safe and high-performing reconstructed soil, deployed for construction, would be a precious resource in efforts to achieve environmental sustainability. Continued monitoring to ensure the soil’s performance will be key. For example, if it was situated close to a water course, and leached a lot of nitrogen, this could have a negative impact on water quality. If monitoring shows that the microbial community in the soil is not fit for purpose, this can be amended. Once the soil becomes `living’ it will need to be assessed at regular intervals to ascertain how well nutrients and other quality indicators are being retained. It will also be important to understand how such soil function in the long term, and to what extent their chemistry and biology should be regulated.
The nutrient content of soil differs depending on land use and management. Sustainable soil management seeks to optimise different functions to increase soil resilience, depending on the main land use. To develop effective solutions there is still much research left to do. Scientists need to embark on extensive monitoring and data collection. This would be helped by employing a whole-system approach involving natural and social scientists, communities, industry and policy makers. Alongside this there is great potential for the construction sector to adopt digital solutions to support soil management. One of the immediate areas where this could be done is with soil tracking. Once soil resources are properly assessed and their reuse is planned, the soil is handled and placed; it is imperative that its location, health and function is tracked throughout the process.
Regulation and policy must keep pace with scientific progress if climate emergency declarations are to become more than rhetoric. Wherever possible and appropriate soil must be considered, by regulators and industry alike, as a resource within a circular economy. Alongside this, ‘soil managers’ (e.g. the construction sector) must act as primary custodians of this resource. Where firms have sustainability strategies, including elements such as targeting zero waste and environmental net gain (often publicly marketed), it is imperative that best-practice soil management is always adopted. To not do so can call into question such strategies and commitments.
Soil management is not the sole task for either government or industry, it is a joint endeavour. CL:AIRE remains committed to helping create the conditions to allow this to happen especially through its DoW CoP.
The time in which environmental stewardship strategies can be developed is limited; it has to happen now.
Defra. (2022). UK statistics on waste. Retrieved from https://www.gov.uk/government/statistics/uk-waste-data/uk-statistics-on-waste
Defra and Environment Agency. (2018). Resources and waste strategy for England. Retrieved from https://www.gov.uk/government/publications/resources-and-waste-strategy-for-england#full-publication-update-history
Environment Agency. (2019). Retrieved from https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/805926/State_of_the_environment_soil_report.pdf
FAO, U. (2019). Soil erosion: the greatest challenge to sustainable soil management. 100 pp. . Rome: Licence: CC BY-NC-SA 3.0 IGO.
Office for Product Safety and Standards. (Regulators’ Code). Regulators’ Code. Retrieved from https://www.gov.uk/government/publications/regulators-code
UN FAO. (2019). Retrieved from https://www.fao.org/about/meetings/soil-erosion-symposium/key-messages/en/
Article prepared by Professor Mark Fitzsimons, University of Plymouth & Nicholas Willenbrock, CL:AIRE
Featured image credited to Cognition Land & Water