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The Pandora’s Box of earthworks and emissions

Civil Engineering By Kevin McGee, Associate Director, Geoenvironmental – 22 November 2022

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Kevin McGee

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The phrase "So long as I know it not, it hurteth me not" was first attributed to the 16th Century English author George Pettie. The irony is he wrote this during the reign of Queen Elizabeth I, who famously oversaw the destruction of almost all of England’s forests, resulting in the first modern energy and environmental crisis.

Times have moved on and attitudes have changed; we now realise that just because we can’t see something doesn’t mean it isn’t a problem, it just makes understanding that problem a bit harder.

Fast forward from Tudor prose to the current climate and biodiversity crisis, and we see real-life evidence that what we can’t see can indeed hurt us. And, like the destruction of the Tudor forests, we don’t always understand it well.

While measuring emissions of methane, carbon and nitrous oxide generated by the construction of a development's above ground components is an increasingly well-quantified and well-informed science, measuring what goes on below the ground before we build remains a bit of an unknown and full of surprises.

As part of Cundall's drive to net zero carbon, we have been developing tools to measure the impact of development in the ground so we can inform decision-makers on the least impactful choices. It turns out that measuring impacts from earthworks is a little like opening Pandora’s Box. Once opened, there are numerous unspecified evils being released which we yet do not understand.

There is an increasing body of evidence from around the world that far more carbon is released from soils and rock during excavation and earthworks than we thought. This is then compounded by the fact that soil, as a living organism, goes through a whole series of complicated changes and processes, so that even when sites are fully restored, they will still have released more carbon and methane than if they had been left alone.

If we then factor in the fact that soils which are stockpiled during construction are far less effective at carbon sequestration than in situ soils, it becomes apparent this element of project works is a significant contributor to greenhouse gas emissions.   

And that is before we even get started on waste, landfilling and aggregates!

As civil engineering and geotechnical designers, we have to be led by the science and the facts. Ignoring the impact of earthworks because they are so often ‘unseen’ and poorly quantified and mismeasured is not an option. We need to work to develop and refine tools to measure the impact so we can invent solutions to mitigate the effects. Because if we don’t, the hard reality is that George Pettie was wrong - what we can’t see very much can, and will, hurt us.