Almost all the potentially frackable rocks in England and Wales lie under aquifers - and their exploitation could their contaminate drinking water supplies.
The British Geological Survey (BGS) in partnership with The Environment Agency (EA) have published a maps which show the depth to each shale gas and oil source rock below principal groundwater aquifers in England and Wales.
Along with the maps, the BGS/EA draws attention to the fact that almost half of the Principal Aquifers, most important for drinking water supply, are underlain by shales or clays that could be used for oil or gas production.
But it fails to mention the most striking fact: that almost all the potentially frackable rocks in England and Wales lie under aquifers - and that their exploitation could their contaminate drinking water supplies.
Where there's oil or gas, there's water
The BGS/EA do not reveal the actual figure, but a simple inspection of the two main maps released today (see image) shows that there is a strong correlation between the presence of oil and gas bearing rock, and that of aquifers.
Only about 5% (by visual inspection) of the frackable resource is in areas without aquifers, in an area centered on Leeds - but even this area is closely fringed by the most important 'Principal Aquifers', whose contamination would pose a severe threat to drinking water supplies for millions of people across the North of England.
Groundwater from aquifers provides 30% of drinking water in the UK and up to 70% of the drinking water in South East England making it one of the most important natural resources in the UK - a resource that needs effective long-term protection.
EA: 'it's all perfectly safe'
The Environment Agency requires fracking operators to produce detailed geological assessments, and hold 'groundwater permits' unless there is no significant risk to groundwater.
"Developments will not be allowed to go ahead if they are too close to drinking water sources", says the Environment Agency, and it "will not permit the use of chemical additives in hydraulic fracturing fluid that are hazardous to groundwater."
However the hazard to groundwater does not arise just from chemical additives, but also from the rocks themselves, which often contain heavy metals and radioactive isotopes of thorium, uranium, radium and radon.
Dr Alwyn Hart, Head of the EA's air, land and water research team said: "We have strong regulatory controls in place to protect groundwater, and will not permit activity that threatens groundwater and drinking water supplies. These maps will help public understanding of the separation between groundwater and potential shale gas sites."
But how safe is it?
The experience of fracking in the US shows that fracking operations can contaminate aquifers by three main routes:
- the spillage or deliberate dumping of contaminated fracking waste water which can infiltrate into groundwater
- leaks in the sides of boreholes
- geological faults deep underground which permit the passage, under pressure, of fluids and gases from the shale rock into higher geological levels.
The first two potential causes are relatively easy to control, but the third is essentially uncontrollable as the existence of these deep faults is generally unknown until the contamination is detected.
- The Principal Aquifers (main drinking water aquifers) are present across a large part (81%) of England and Wales.
- Shales and clays which have potential for shale gas/oil are present over more than half (51%) of England and Wales.
- Almost half (47%) of the area where Principal Aquifers are present is underlain by one or more of these shales or clays.
- The Bowland Shale, an important potential target for shale gas development, is generally (92%) at least 800 m below the Principal Aquifers actively used as a source of drinking water.
- There are six Principal Aquifers above the Bowland Shale. These are: the Chalk, Lower Greensand, Corallian Limestone, Oolite, Magnesian Limestone and Triassic sandstones.
- The Chalk aquifer of the South Downs is above part of the area in The Weald Basin identified as prospective for shale oil. In this area the uppermost shale oil source rock (Kimmeridge Clay) is at least 650 m below the Chalk. See figure below.
Dr Rob Ward, Director of Groundwater Science, British Geological Survey said: "For the first time the public will be able to visualise our nationally important Principal Aquifers in relation to potential shale gas and oil source rocks. This information will help to better understand the risks to groundwater from shale gas and oil."
The maps and data are freely available from the BGS website.