We had a lot of interest both in the region and from national press (Independent, BBC Radio 5 Live) about the notion of a new “Mine on Tyne”, in the very same area where our geothermal borehole was drilled: in the heart of the 24-acre ‘Science Central’ site, which will be built-out over the next decade or two to become both an exemplar of a modern sustainable built environment and the place where the University’s sustainability research is headquartered.
“So what’s all this about turning the site into a coal mine? Have you lost your minds?”, I hear you ask.
Well, we reckon not. The story is as follows:
As everybody knows, Newcastle is the global birthplace of ‘Carboniferous Capitalism’ – the industrial-scale exploitaiton of fossil fuels, and its insertion into a global export economy. As a consequence, much of our city is underlain by a warren of old colleiry workings. Under our particular site, the last of these to be excavated were at depths of hundreds of metres in the 1940s. These deep old workings are not a particular problem. What is a problem are the extensive mediaeval workings in the two shallowest coal seams – the High Main Seam and the Metal Seam – which were extensively worked using primitive techniques (leaving lots of coal behind to support the roof) as long ago as the 13th and 14th centuries. As you go up the hill from our site these two seams quickly become buried beneath so much overburden that they are no longer a threat to surface stability, but by a quirk of geography right under our site they are both within 20m of surface. They are riddled with old workings in various states of partial collapse. These unstable old voids have particular potential to damage future buildings on the site. A further risk – though thankfully less likely – is that of the remaining coal catching fire. This happened in the shallowest seam in the Fenham area in the 1700s, and fires raged across the city for 50 years. Here we have a classic example of unsustainable development: our forebears did not leave the site in a condition that gives us full freedom of choice over how to use the ground.
So what can we do? One approach would be to inject a cement-based grout into the old workings. At the very least this would require 50,000 cubic metres of cement, possibly much more. Now cement production is one of the most carbon intensive industries and the carbon footprint associated with this would be significant, with a CO2 equivalent in excess of 330,000 tonnes. The coal itself, if taken and used, would release about 160,000 tonnes of CO2 – less than half that produced by the cement. Counter-intuitively then, in this quirky case, removal of the coal is the best option from a climate change point of view. It also totally eliminates any risk of accidental fire in future. The plan is, therefore, to remove the surface layer of rubble, take out the remaining coal and then put the rubble and other rock fragments back, compact them and thus create a permanently stable, non-combustible platform for all future buildings.
There are a couple of ancillary advantages to taking this approach. As already indicated, the workings here could well prove to be as old as 13th century, dating back to when the local monasteries were granted leave to work the coals on ‘Elswick Moor’. We might well be fortunate and find some archaeological remains from this ancient period of mining.
Of more relevance to the here-and-now, and to our plans to provide energy to this site in future from geothermal sources, is the possibility the coal removal and backfilling operation offers us to install ground-source heat loops in the subsurface of the site. With these in place, we will not only be able to take advantage of high temperature water from the deep borehole (which will be carefully worked-around if the coal extraction is given the go ahead); we will also be able to supplement this with shallower sources of heat from the subsurface and, crucially, provide cooling for buildings on the site in future as well (something the deeper geothermal resource does not offer so readily). We would therefore be in a position to develop the UK’s first ever system combining the virtues of deep geothermal energy with heat pump-based ground-source heating and cooling. That’s the real prize for the long term.