The quarry itself lies within very unstable land. It is within the major fault zone of the Seaham Harbor, Newbottle and Houghton Cut Faults. While the limestone was being quarried out of the land surface, the layers of coal underneath were being mined out in 6 seams. It's plain logic that if you gouge out great areas of coal underground, then the land up above is going to collapse to fill the underground hole. But it isn't as simple as that; things rarely are. How the land collapses depends on how you take the coal out. Take it out in one fairly clean sweep and the collapse, or “subsidence”, will take place soon after, or at least within a matter of a few years.
When the rock collapses underneath the landfill, the polyetheline liner will be left suspended with many tonnes of rubbish pressing down. It may stretch for a while but sooner or later inevitably it will give way. We all know what happens when a full bin bag collapses on the way to the dustbin.
The other effect is that the mining-induced movement which has widened the joints in the limestone has the result that the water flows even faster on its way to the pumping station. This is the “Aqua-Super-Highway”: a high speed route.
Here are some more pictures which show evidence of instability and subsidence which were taken in, or very near the quarry:
As you look at them all, ask yourself: "Does this look like a good place to put millions of tonnes of waste that's right on top of the water supply?"
This huge crack appeared on the A690 road, just metres from the quarry. If the unstable ground can do this to tarmac and road building materials, what do you think it would do to a 2mm thick plastic liner?
So is it possible to have a safe landfill site?
Yes, as long as it’s:
1. Constructed in the right place,
2. Constructed in the right way, and
3. Run safely.
Do any of the above apply to Houghton? Let's see:
Firstly, find a safe place. This is preferably an old clay pit which still has a good depth of clay in it. This stops nasty stuff that is dumped in it getting out. No old clay pit handy? Then find another safe site in stable land, nowhere near any rocks which are used for water supplies, away from where people live and give it a good thick lining of clay. Does Houghton Quarry fall into any of these categories? No. It is in unstable land, within the water supply and in the middle of the town.
Secondly, construct it properly. If it isn't an old clay pit it will need a good thick liner of engineered clay. In Houghton, the quarry is huge with a boundary of 2 kilometres. To fill it with rubbish, Biffa split it up into filling areas called “cells”. These are all interconnected so it doesn't matter if one part is reasonably well-constructed if another area is a pig's ear. Let’s look at the area called Cell 1.
The “clay” used is 1m thick with as little as 10% clay in it. It is Magnesian limestone-based, highly reactive with acids. It contains large boulders and planks of wood. It was tested repeatedly until a sample could be found to pass as suitable, then the whole section counted as “ passed”. The Agency says that 10m to 70m thick clay compacted by the Ice Age on the surrounding countryside lets 25% pure rainwater soak through. Yet they claim the clay in the Quarry will stop all leachate “chemical soup” soaking through.
I think we all know the answer to number 3...