What are the environmental concerns with shale gas production?

Several environmental concerns have been raised pertaining to shale gas exploration.

Drinking Water Contamination

In the US, where well water is often used in rural areas as drinking water, high concentrations of dissolved methane have been reported. A recent study by Duke University in the Marcellus Shale Play in Pennsylvania, USA suggests concentrations of methane in groundwater increase with proximity to a shale gas well ^[6]. They suggest this is most likely due to faulty well bores or abandoned, uncased wells from previous decades. The UK Environment Agency echo this.

It is worth noting that methane occurs in groundwater in some areas of the US and UK, in large enough quantities to cause explosions ^[7].

Scene from the 2010 Documentary "Gasland" showing a man in Colorado, USA lighting methane in his tap water. This particular case has been proven to be naturally occuring methane^[25].

The flowback fluid, which is the fluid that comes out of the well after fracking contains not only the chemicals added to compose the fracking fluid but also dissolved chemicals from the shale itself. It can even contain a mixture of radioactive elements, called NORM (Naturally Occurring Radioactive Material).

In the US, flowback water has been allowed to stand in open (lined) pits near the fracking site, where it could pose a threat to surface water (during heavy rain, for example). Current operations involve the water being stored in tanks and being taken away for treatment at a specialised plant near Manchester, however, the Environment Agency has not ruled out lined pits - this would be assessed site by site.

The chemicals in fracking fluid have also been cause for concern, however, the same study by Duke University shows no sign of fracking chemicals in groundwater. A report by the Tyndall Centre, however, suggests that faulty cementing on wells - and certain states in the US do not require full cementing of well annuli (GWPC) - could provide a path for migration of fracking fluid retained in the rock to the level of aquifers^[8].

In the area of Lancashire where fracking is being carried out, the Environment Agency have deemed that there are no vulnerable near surface aquifers. Indeed, in the North-West of England, rainfall is fairly high and only 11% of drinking water is sourced from groundwater ^[9].
Water Usage

Fracking uses a considerable amount of water, and estimates vary enormously depending on the source and the depth of the well, the permeability of the rock and other factors. Cuadrilla estimate that 13 million litres (Ml) of water could be used for the fracking of one well.

The Tyndall Report extrapolates 560 - 1,300 Ml per year would be necessary to supply 10% of the UK's Gas over 20 years. This is in comparison to the 3,802,000 Ml abstracted yearly by the energy industry in the UK.

Critics say this could place strain on water resources, especially in the South-East or other areas in which water is scarce. However, the EA have found that the water use is relatively small compared with public supplies and would not pose a risk to water resources.
Fugitive Emissions

Fugitive emissions are losses of methane from between the well cap to the end user. These can be due to leaks in pipelines, venting from pressure valves and so on. These are likely to be the same as from conventional gas. However, the fugitive emissions from the fracking process are of more concern, as they have not been examined in detail and could potentially be very high

After fracking, before the well is capped and the gas piped away for use, the well may produce methane that is not profitable to store or transport. Robert Howarth or Cornell University has calculated, based on EPA estimates, that the venting of such emissions could mean shale gas may be actually worse for global warming than coal.^[10]

Graph from Cornell study. Low and high estimates of fugitive emissions from various fuel sources

Coal releases more carbon dioxide per unit energy than natural gas, but methane is a far more potent greenhouse gas - 72 times worse per unit mass than carbon dioxide over a 20 year period, falling to 25 times as much over a 100 year period. The EA believe, however, that good practice can mitigate such fugitive emissions, and are considering options for monitoring air near the site to keep track of any leaks.

Furthermore, venting is an extremely dangerous procedure and would most likely be restricted by the HSE. Cuadrilla plan to flare the gas collected during testing before capping.
Landscape and Local Disruption

As with other industrial sites, during the well construction, completion and stimulation phases there will be heavy road traffic. The Tyndall Centre estimates 4,300 - 6,600 truck visits based on a well pad of 6 wells, 3,900 - 5,800 for the fracking alone ^[8]. This could lead to deterioration of local roads.

The landscape impact of drilling sites is also a problem exacerbated by the high population density in the UK. The population density of Lancashire - 472 people per square kilometre - is thrice as high as New York State, four and a half times as high as Pennsylvania and twelve and a half times as high as Texas.

This problem has been addressed by situating up to 6 wells on the same site ("pad") and drilling horizontally away from the pad. Nevertheless, to supply 10% of the UK's gas consumption, which is what the ECCC suggests shale gas could provide, the Tyndall report estimates 2,500 - 3,000 wells need to be drilled over a 20 year period. ^[8]

A large drilling rig is also constructed, which is unsightly and can be noisy. This, however, is only temporary - drilling lasts only a few weeks. After drilling and fracking, the rig is replaced by a "Christmas Tree" well top.
Earthquakes

It is well known and documented that injecting fluid underground at high pressure can lead to tremors. Injecting fluid either fractures the rock or moves into existing fractures. The normal stress between the two faces of the fracture is reduced due to the hydrostatic pressure of the fluid in between (it is helpful to imagine the fluid floating the rock). Therefore the friction force that keeps the rocks from moving, which is proportional to the normal force between the two faces is reduced.

This leads to movement of the two faces relative to each other, which is recorded as seismic activity. It is not to do with movement of faults, although this does cause earthquakes in the UK occasionally.

Diagram to show earthquake mechanism. On the left, the friction force balances the transverse stress component and the rock does not move. On the right, hydrostatic pressure acts against the normal force and the friction force is now less than the transverse force; the two faces slip against each other.

It is worth noting that the majority of earthquakes in the UK are induced - mainly from coal mining. The magnitude of the earthquakes was surprising to the DECC, but was not large enough to cause damage. Because shale is a soft rock, it is unlikely that powerful, damaging earthquakes will be induced.

The only outlier is a magnitude 4.7 recorded in Arkansas, USA, where both fracking fluid and waste water from the well were being injected subsurface; it is not clear which operation, if either, caused the earthquake. Links to hydraulic fracturing there and in Texas have led to a fracking moratorium in Arkansas^[11].

According to Professor Peter Styles of Keele University, who is investigating the earthquakes with the BGS, the link between hydraulic fracturing and seismic activity can be exploited to some extent to mitigate the risk of a serious earthquake that could cause damage to property and the integrity of the well bore. Seismic activity can be monitored and fed back into production so that if seismic activity were to intensify, fracking could be slowed down or halted.

The integrity of the well bore is crucial in ensuring no fracking fluid or shale gas is allowed to contaminate the surrounding rock, in which there may be an underwater aquifer. In the case of Cuadrilla's operations, they will pressure test each casing string when it is installed and can perform a remedial cementing if there proves to be a breach.

In much the same way as the gap between lightning and thunder indicates the distance of a storm, the short, half-second delay between the P and S waves indicated that the epicentre was close to the seismometer. It was shown to come from around 3.6 kilometres below the site, where fracking was being carried out.

The World Wide Fund for Nature recommend a halt to fracking activities in the event a link be validated, unless the magnitude of future earthquakes can be proven to be insufficient to cause damage to property or to the integrity of the well bore.
Who Manages The Risks

In England, Wales and Northern Ireland, the Environment Agency (EA) is in charge of managing the environmental risks of gas drilling onshore and up to one nautical mile offshore (see below). They would be informed of the chemicals used in the fluid and could require the operator to apply for a permit.

They would also be initially testing flowback water from the site, although Tony Grayling, Head of Climate Change and Communities at the EA, stresses that this is the responsibility of the operator and would require them to carry out testing in future.

If they assess the site as posing a risk to groundwater, a permit would be needed. They would consider all risks, including seismic activity, in their decision as to the necessity of a permit as well as whether to issue that permit. Of the 5 sites currently with planning permission in Lancashire, three have been assessed as not needing a permit and two are as yet unassessed.

Measures that are currently mandatory for all fracking sites are an impermeable membrane to prevent spills entering the soil, and bunding to contain leakages.

Shale well with blowout preventer, drainage dyke, bunding and gravel over impermeable membrane. Courtesy Cuadrilla Resources Ltd.

The Environment Agency believe that a blowout such as that in April in Pennsylvania, USA, would be very unlikely, as the above measures, as well as such conditions that are attached to planning permission at the discretion of the EA or the local authority, would make it extremely difficult for such an accident to occur. In the case of a spillage, the EA have powers to ensure action is taken to protect the environment.

The EA are looking at options for monitoring the fugitive emissions of methane to the air, however, since this poses a risk to the human operators as well as the environment, this risk is managed by the Health and Safety Executive (HSE). The HSE will be satisfied by the companies proposal and will ensure appropriate checks, for example of well integrity, are in place if necessary.

If offshore shale gas drilling were to take place, the environmental risks would be managed by DECC and the Marine Management Organisation.