What you need to know about soils reuse

Have you ever thought about using existing site soil as a resource? As the world’s interest in reducing carbon rapidly increases, we are finding more and more clients actively considering this option. I mean... it’s already there, you probably need to move it one way or another to develop the site. Reusing site soil is the lower carbon, lower cost solution.  For several years, our ground engineering team has been looking at reusing soil, and it can be trickier than you might assume to reuse soils already present on your site. I will break down below various things that you should account for to make the best use of existing soils on your project.  

First off, not all soils are created equal. Depending on the site’s history and environmental setting, soils could be of risky chemical quality or not be geotechnically suitable for the proposed end use. Similarly, whether soils are suitable for reuse will be dependent on the context in which they’re intended to be used. Each site will be different and should be treated individually, this is not one size fits all. In the UK government's ‘brownfield first’ approach, as technical specialists, we are seeing increasingly complex soil reuse scenarios coming across our desks. Whilst these can be challenging, they also bring a sense of fulfilment, as they are incredibly important to reducing carbon.  The second factor to consider is how you go about proving that your soils reuse isn’t a waste disposal activity. The Waste Framework Directive defines waste as “any substance or object which the holder discards, or intends, or is required to discard”, on that basis waste isn’t defined by its properties or its suitability for reuse, its only defined on the behavioural intention of the holder. Waste isn’t a technical definition when it comes to soils, it’s a legal one.  

What really is the difference between reusing soils and illegally fly-tipping them on your site or under your shiny new building? Your paperwork. As with everything that has the potential to become a legal matter, the devil is in the detail. The paperwork is what will prove that you have implemented all the appropriate tests and measures to ensure that what you have created on your site is not, in fact, an illegal landfill but a suitable, well-designed development platform. Generally, your reuse activity will fall under one of three categories: natural soils from uncontaminated sites; soils that are already a “waste” in the eyes of the law and need appropriately permitting; and soils in between, with some potential contamination that are not currently waste and shouldn't become waste during construction.

For uncontaminated, naturally occurring materials arising from construction activities where it is certain that the material will be used for construction purposes in the natural state from which it was excavated (i.e, do not require treatment); these soils are specifically excluded from the Waste Framework Directive. I would still advise having evidence that these are uncontaminated and naturally occurring; however, for the purposes of the waste legislation, no specific regulatory regime needs to be followed.  

For materials already classified as a waste, such as those deposited under landfill licences, other demolition wastes (wood/glass) and colliery spoil materials - these require an Environmental Permitting route to be followed. This permitting route will be regulated by the relevant authority (Environment Agency in England and Wales, Environmental Protection Agencies in Scotland, Northern Ireland or Republic of Ireland). The type of permit required will depend on the volume and nature of the materials. You may find there is an exemption or regulatory position statement in place for your circumstance, meaning a full permit process is not required (although generally the activity will need to be registered). At the other end of that scale, you may find yourself looking at a Bespoke Deposit for Recovery or Landfill permit. All of these require different volumes of information to be collated and submitted and with varying levels of regulator input, can take anywhere from a month to a couple of years to get the right permit in hand. Knowing this early is key to protecting the project programme and not having to choose between material reuse and costly disposal.  

For potentially contaminated soils, made ground materials, dredgings, ground based infrastructure that is capable of reuse within earthworks projects (e.g. road base, concrete floors) and aggregates as a result of demolition activities, the Definition of Waste Code of Practice (DoWCOP) administered by CL:AIRE is a voluntary scheme used to follow a non-regulated route for soils reuse in England and Wales. This scheme relies on the use of a Qualified Persons (QP) instead of a regulator to ensure all your paperwork is in place and that the works being undertaken are in line with the code of practice. As a QP myself, championing the DoWCOP scheme is not hard, it is a robust, risk-based approach that is applied to low-risk sites in a way that takes pressure off the regulator and removes some of the “red tape” for developers. The DoWCOP scheme has four key factors; Protection of Human Health and Protection of the Environment, Suitability for use (without further treatment), certainty of use and quantity to be used.

Under the national planning policy framework, developers have a responsibility to prove to the local planning authority that their development will not cause any harm to people or the environment and will be “suitable for use”. This often means that your site will have a remediation strategy that defines what suitable soil looks like. In addition to chemical suitability, your soils must be physically suitable for use; this information would typically be found in an earthworks strategy or specification. Defining your suitability criteria ahead of the works gives weight to the body of proof that you intend to reuse soils that meet that criteria, therefore, you can’t be intending to discard them. Both documents would be required for reuse of soils under the DoWCOP, and would rely on pre-requisite risk assessments for both Human Health and the Environment.  

In addition to proving that materials are suitable for use, there is also a need to prove that you have a need for them, a certainty for their use. You can’t just use material because you have it and its suitable; there needs to be a technical need for the material. Early planning is key to providing that certainty of use. If an acoustic bund wasn’t in your original development but one appears, using the volume of material you would otherwise have been required to dispose of, that would bring your certainty of use into question and potentially be seen as a disposal activity carried out illegally.  

Soils reuse legislation is still catching up with the zero carbon principles that we have come to realise are so important in the 15-20 years since this legislation was introduced. With the proposed landfill tax changes coming into force soon (see article by our head of geoenvironmental engineering Kevin McGee here) there is even more reason to consider the circular economy of soils on your projects. Early planning is key; soil quality and reuse should be part of the design considerations from the outset, and it is important to acknowledge that not all soils are created equal.