WITH the granting of fracking licences in north Cheshire, I wonder how any extraction of shale gas will affect the layers of rock salt above them?

In the late 19th century the pumping of water into these salt layers produced brine, which could then easily be brought to the surface.

However, this process produced underground holes which led to major subsidence across a large part of this area.

We still have the new lakes or “flashes” with us today, even if the damage caused to property is now mainly recorded in photographs that can be seen at the Salt Museum in Northwich.

My understanding is that fracking will again involve pumping fluids at very high pressure down into the earth, and at a level much deeper than where the salt deposits are.   A year or two ago, when exploratory fracking was carried out in Lancashire, small earthquakes were recorded as the deep rocks were fractured.

No significant property damage was then reported, but if a larger commercially viable fracking operation was started underneath the Cheshire salt beds, might there be a chance that damage would be caused to these beds?

Nearly all modern salt extraction in Cheshire is carried out using the room and pillar method. This means only a proportion of the salt beds are removed, with the rest (the pillars) being left in place to make sure the rocks above don’t collapse.   These pillars currently keep Northwich and the River Weaver from disappearing into the earth.  If deep level fracking was carried out that led to earth movements below the salt, would there be a risk that these pillars of salt might be damaged? If that happened, significant subsidence at ground level would be probable.   Much more serious would be a pillar collapse under the River Weaver or its tributaries.

If this happened and significant amounts of surface water penetrated the salt beds there would be a real problem, as the water would simply dissolve the salt pillars.

These salt beds are roughly 75ft thick, so imagine Northwich town centre dropping 75ft. Imagine the salt mine at Winsford dropping 75ft.

Also, there is the new natural gas storage facility being built locally. Might this be susceptible to collapse if subsidence led to water pouring in?

I know I’m being alarmist, and I’m sure the people involved know what they’re doing, but would whoever starts fracking underneath us, please be very careful.

Allan Jones Knutsford