This blog is written by David Walls, a PhD researcher studying minewater geothermal at the University of Strathclyde (@FafFclyde). When not at work, David can be found running, swimming or cycling somewhere in Scotland. Get in touch with David on LinkedIn.
I love rocks, I love the planet, and I love being physically active. Thankfully, I am lucky enough to combine all three in my research in the fascinating and expanding world of geothermal energy. Geothermal resources are typically associated with explosive volcanic landscapes like Iceland or New Zealand, but my research explores how the cooler (and calmer) geology in Scotland can be put to good use for low carbon heating and cooling. I spend my research time between various field locations across Scotland, the university laboratories and, of course, at my ‘working from home’ desk.
For my PhD, I’m working to assess how much heat could be tapped from former coal mines in Scotland, and which are the most promising mines. Whilst these types of geothermal systems are becoming increasingly popular, many people (including me when I first heard of the idea) struggle to picture how they work. If that is you, then do not worry; the legacy of coal mining across much of the UK is hidden beneath the ground out of sight. But in ex-mining areas, beneath your feet, there might be deep vertical shafts and underground tunnels, some large enough to walk an elephant through.
The ground beneath us (particularly in Scotland!) contains lots of water. When coal was being mined, large volumes of water had to be pumped to the surface to keep the miners dry and safe as they dug out the coal. When the coal mines were closed, pumping stopped, and water flooded the mined-out voids as the water table recovered back to its previous, before-mining level. Some forward-thinking scientists saw that if coal minerals, water and air were allowed to mix, then polluted water could leak out at the surface. Sure enough, they were right, and contaminated mine drainage disasters occurred across the country, sometimes spewing vast volumes of bright orange iron-rich water into scenic valleys and rivers. Nowadays, the worst of these discharges are treated to avoid further environmental harm, but many still flow into UK watercourses. Whilst these discharges are by no means hot, they average around 10 ℃, and this is warm enough to be used to heat buildings when boosted with a heat pump.
It became my task to find as many of these discharges as I could. I wanted to know the water chemistry, temperature, and flow rate of the discharge. Once you estimate how fast the waters are flowing, you can begin to find out how much heat minewater discharges could provide to houses or businesses nearby. The chemistry helps you to understand what engineering challenges you might face if you use the water, like corrosion or clogging of pipes.
It all began when I read a chapter of a book* which stated that Scotland had 167 discharges from mine workings, which covered 180 km of rivers channels with orange iron oxide precipitation (known as ochre, which you can see in bright orange in the stream beds in the photos). Once I had found the source of this information- a spreadsheet from the Scottish Environmental Protection Agency- I realised the scale of the task. There were 160 entries, each of which only supplied a site name, and a 6-figure grid reference… that’s an area of 100 m by 100 m, for 160 sites. That’s 1.6 million square metres (almost 300 football pitches) of area to be searched, and without guarantee that the discharges even continue to flow or could be found!
The challenge was on, and to stick to my low carbon values, include one of my favourite hobbies, and make sure I had a healthy dose of physical activity and sunshine, I decided to visit each site via bicycle. All of this was thoroughly risk assessed and signed off with safety measures and emergency plans. After a total of 14 days on my bike and 800km of cycling and searching, I was confident that I’d done all I could to scour the landscape and was delighted to have successfully found 60 discharges. I was equally delighted to discover that my PhD could involve such adventure and exploration, away from being in the lab or sat at my desk!
Discharges were found by the sound of cascading water, a flash of bright orange amongst green vegetation, or by using my nose to follow the rotten egg smell (caused by hydrogen sulphide gas) found along with some minewaters. In one instance, there were bright orange pawprints from a dog which seemed very happy with itself, leading right to the ochreous source! (the owner seemed less impressed and wasn’t looking forward to the clean-up task…). Unfortunately, some of the original discharges remain unfound, and some were found but deemed too dangerous to access. Others brought with them slices of history in the form of old mining buildings and structures nearby.
Once each discharge was located and had a more accurate grid reference assigned to it, I was able to return, along with some cheery field assistants, to collect minewater samples to test for chemistry in a lab, and take other measurements to determine its potential as a geothermal resource.
When all the discharges, large and small (from less than 1, to over 100, litres per second) are added up, they have the potential to heat thousands of homes. As a result, this work has already been used to influence decisions about low-carbon heating projects across Scotland.
It is amazing to think that contaminated mine discharges, which historically have been a nuisance and environmental concern, can now be considered as a low carbon heating solution. With uptake of this resource, we can celebrate the legacy of old mining towns across the UK and make positive steps to tackle carbon emissions, fuel poverty and environmental contamination.
*Younger, P.L. 2000. Iron. Darcy, B.J.D., Ellis, J.B., Furrier, R.C., Jenkins, A., Dies, R. (eds) Diffuse Pollution Impacts, Terence Dalton Publishers, Lavenham, for Chartered Institution of Water and Environmental Management, 95-104.