Managing contamination risks

Operators will need to learn from US experience and give top priority to avoiding groundwater pollution, finds Simon Evans

Many studies have been carrie dout on the wells in the US Marcellus shale. Credit: RUHRFISCH (Talk)/ GFDL CC-BY-SAA new technology for extracting gas arrives in the UK with the risk of seriously polluting water and air. It is only after rapid early growth that the problems begin to appear, with a surge in incidents and several million-litre waste spills.

The Environment Agency puts the rise down to the sector’s rapid expansion and its use of unfamiliar technologies.

This is no crystal ball-gazing exercise but a summary of the latest events in anaerobic digestion (AD), with one February spill in Shropshire involving up to eight million litres. The AD sector is often pointed to as a greener alternative to gas extraction by hydraulic fracturing.

Yet both produce methane through technology fairly new to the UK and both involve the storage of large quantities of potentially dangerous liquid wastes on site.  These may find their way into groundwater stocks or surface water.

In its August 2013 risk assessment of shale gas, the agency lists spills of concentrated chemicals prior to mixing into fracking fluid or the loss of the fluid itself as high pollution risks.1

It says: “Our experience of regulating industrial sites is that accidents can and do happen.” These types of surface spills are one of the most likely causes of shale gas pollution incidents and are one of the top three fracking risks identified in an AEA report for the European Commission.2

Cuadrilla aims to minimise the risk of spills entering the wider environment by giving well pads an impermeable plastic liner and soil bunds to contain liquid accidents. Planning permission at its Balcombe site for instance, requires bunding and liner to be able to contain up to 110% of the contents of all storage tanks and pipework.

Flowback fluid returning from underground after the fracking process is complete will be captured and stored in closed steel tanks rather than the open ponds which have sometimes been used by US frackers and the UK AD industry.

The fluid has high salt levels and a range of heavy metals and naturally occurring radioactive materials (NORM). At Cuadrilla’s Preese Hall site near Blackpool, the fluid was some three-times saltier than sea water and had up to 179 micrograms of lead per litre against a 10µg/l drinking water standard. It had chromium at up to 222µg/l, more than four-times the drinking water standard.

The Environment Agency will consider this flowback fluid as waste under the 2006 EU Mining Waste Directive, meaning a waste management plan will be needed showing how it will be minimised, reused and disposed of.

In a series of letters sent during mid-2012 and released under Freedom of Information rules this August, Cuadrilla argued that the flowback fluid should be considered a non-hazardous product of “prospecting” activity, exempting it from the directive’s management plan requirements.

The agency did not agree and in any case the exemption would not apply to full-scale shale gas exploitation.

Sustainable options

The agency says it expects reuse of the fluid following treatment and blending with extra fresh water to be the preferred and most sustainable option, but it recognises this is unlikely during exploration.

Instead, the flowback fluid will be tankered off-site for treatment. Cuadrilla’s Preese Hall site is the only one to have fracked in the UK and until October 2011 its waste water was sent to United Utilities’ Davyhulme sewage treatment works in greater Manchester, which has a permit to accept industrial effluent.

From 1 October 2011, an amendment to environmental permitting rules means waste containing NORM above certain limits requires a separate permit during handling and disposal. United Utilities decided not to apply for such a permit.

Limits are set for each radionuclide and their sum. For radium-226 the limit is one becquerel per litre. Drinking water with this level for a year would deliver a dose of radiation equivalent to one transatlantic flight.

But flowback water at Preese Hall was up to 90-times more radioactive. The agency says experience suggests the limits will almost always be exceeded for exploratory fracking operations because of the NORM in oil and gas-bearing strata.

Once more substantial quantities are generated, treatment of NORM could become a tricky issue. Its chemistry means that like heavy metals, NORM is likely to accumulate in sewage solids rather than in liquid effluent and this could be at odds with sludge recycling to land. As a result, pre-treatment of fracking fluid might be needed.

Cuadrilla and its waste adviser Remsol say tests using 80,000 litres of Preese Hall fracking fluid show an acid-alkali -pre-treatment is suitable. This would precipitate out NORM in a solid cake containing 90% of the radioactivity and much of the heavy metals.

Lee Petts, managing director of Remsol said he expected the solid waste to contain less than 5Bq in total per gram meaning it would be exempt from radioactive substance rules and could be sent to a standard non-hazardous waste landfill. The liquid fraction could then be discharged into the sewer system, he says, subject to permit conditions.

However, a recent study from North Carolina’s Duke University found stream sediment below a treatment plant in Pennsylvania contained radium-226 above US radioactive waste thresholds, even though the treatment process reduced radium levels by more than 90% compared with raw flowback water.3

Reuse of flowback water, as favoured by the Environment Agency and Cuadrilla, would reduce the amount of waste and cut demand for fresh water but might make treatment more difficult.

Estimated fresh water use in the US fracking industry runs into hundreds of billions of litres per year, although this amounts to fractions of a per cent of US water consumption.

For the UK’s nascent industry, estimates of water use vary wildly. DECC says each well requires 10-30 million litres to frack. The International Energy Agency gives a wider range from thousands to 20Ml per well.

The Institute of Directors (IoD) suggests UK fracking water demand could reach an annual peak of 5.4 billion litres.4 This would amount to 0.05% of current total abstractions in England and Wales or about 35,000 average homes. The UK’s water industry has commissioned a two-part study of the risks and opportunities presented by fracking, including an attempt to firm up these estimates.

Dr Jim Marshall, policy and business adviser to sector trade body Water UK says: “If we get it wrong then water has the potential to stop the [shale] industry in its tracks.”

The study’s first part will be finished in a matter of weeks. It will include estimates of fracking’s water demand which are in the same ballpark as those from the IoD, says Marshall.

“It’s not a huge amount of water on a national scale but it’s the impact that may have at local scale in areas already at their abstraction limit,” he adds. This includes the mid-Sussex Weald basin in the Southern Water and South East Water regions, both classed by the Environment Agency as under ‘serious’ water stress.

United Utilities is supplying Cuadrilla with water in Lancashire and although the river Fylde catchment where fracking sites are concentrated is over-abstracted, the firm’s draft 2015-2040 water resource management plan says it does not expect fracking to impact on its overall water resource.

Other firms that could be affected include Welsh Water and Yorkshire Water, both classified as not water stressed. The impact of shale gas is probably not well enough understood to be properly included in the current round of water resource management plans, Marshall says. Revised plans will be due in another five years.

But plans already include scenarios for growth in demand, so adding in fracking is “in some ways business as usual in terms of planning for new industrial or residential developments”, Marshall says. Because of the implications for its members, Water UK is lobbying to get water firms made statutory consultees on fracking planning applications.

The second part of the water industry study, due to be finished next spring, will look more closely at wastewater treatment issues. The IoD report estimated 1.6 billion litres of flowback fluid might need to be treated, about 0.05% of current wastewater treatment capacity. But a lack of baseline data means none of these US studies can prove fracking caused the contamination they found.

This figure is subject to wide uncertainty. Levels of fracking fluid reuse are not yet known and the proportion of fluid that returns to the surface rather than remaining underground can be anything from 10-80% of the injected volume, depending on geology.

Out of sight

What happens to that lost fluid along with the fracking additives and natural contaminants it contains is a key environmental concern – one of the top three identified by AEA’s report for the commission.

Dr Rob Ward, the British Geological Survey (BGS) head of groundwater science says: “If groundwater becomes polluted it can take an extraordinarily long time to clean up. It’s quite hard to do and is very costly. So the key message is don’t let it get contaminated in the first place.”

The agency concurs, saying: “We aim to prevent pollution of groundwater in the first place rather than having to restore it later.”

It will object to fracking within primary groundwater source protection zones where the travel time to a drinking water borehole is 50 days or less. Where fracking would drill through a groundwater resource it will expect best available techniques (BAT) to be applied.

Experience in the US suggests groundwater contamination can happen. Professor Rob Jackson from the US-based Duke University has studied hundreds of wells over several years in the Marcellus Shale.

He found people living within a kilometre of shale gas wells were much more likely to have natural gas in their water.5 A study from the University of Texas found elevated arsenic and other heavy metals in 100 private wells near fracking sites in the Barnett Shale.6 The US Environmental Protection Agency has also found elevated arsenic levels associated with fracking sites.

Jackson says he has not found evidence of fracking chemicals or natural contaminants migrating into drinking water, though he speculates that lighter, more buoyant methane could be a “harbinger” of slower-moving contaminants.

Either way, the agency must be told the identity of fracking additives and will only allow use of non-hazardous substances defined in accordance with the 2006 EU Groundwater Daughter Directive. The identity of chemicals will normally be publicly available “subject to appropriate protection for commercial sensitivity”, says DECC.

Cuadrilla has permission to use three chemical additives. Gluteraldehyde is a biocide added to control bacteria, also used to disinfect medical equipment. Polyacrylamide is used to reduce friction underground but also used in some sewage treatment works. Dilute hydrochloric acid is used to stop limescale build-up but also to control pH in drinking water treatment.

So far only polyacrylamide has been used. Although making up only 0.04% of the fracking fluid, the quantities of water involved mean several tonnes were injected at Preese Hall.

Once below ground it is conceivable that contamination might migrate upwards from the depths where shale deposits are being exploited through fractures in the rock. However, the Bowland Shale in Lancashire is at least 2km below the surface.

A widely cited UK study of North American data found that very few natural fractures extended beyond 700 metres vertically and it was “extremely rare” to go beyond 1,000m.7 Within the next few months Dr Ward hopes the BGS will be able to publish 3D maps of the country’s shale resources in relation to aquifers. This work is being done with the agency and will include the vertical separation distances between shale and aquifers.

The risk of groundwater being contaminated by gas or pollutants migrating upwards from fracked shale beds is minimal where the vertical separation is at least 600m, the Environment Agency says. But vertical separation from groundwater is not the only requirement for safe operation.

Ward says the key pathway identified by US studies of drinking water methane contamination was poor well integrity. This was probably a “legacy effect” of the lack of regulation in early US exploitation, Ward says. “If you’re drilling through an aquifer you have to know you are not creating artificial connections between groundwater at different levels.”

As a result, the integrity of the concrete well casings that separate the gas borehole from their surroundings emerges as perhaps the single most important factor in long-term environmental damage limitation.

Professor Hwyel Thomas, a member of the Royal Society and Royal Academy of Engineering team that produced a major report on shale gas says: “The focus was on well integrity as the significant issue we were concerned about. Careful inspection and management [is necessary].”

A review of well safety for the agency identified best practice as including multiple layers of casing at shallow depths and rigorous monitoring and pressure--testing requirements to ensure seals are not breached.

The agency will ask for details of well and casing designs as part of an application giving borehole drilling notice under the 1991 Water Resources Act.

The agency notes research showing that a “significant percentage” of offshore well casings have “some degree of integrity issues” and that there is similar evidence for US onshore wells. “However, our well casing report shows that [the Health and Safety Executive’s] design and construction requirements provide a very high degree of environmental protection.”

The agency will require fracking firms to carry out environmental monitoring as part of their permit conditions. The checks will be able to compare levels of methane and other groundwater contaminants with baseline data being gathered by the BGS since early 2012.

Results are in for the north-west and south-east where fracking exploration is already on the table and further areas will follow. “We will have coverage of all fracking areas,” says Ward.

BGS will also check levels of trace organic contaminants, Ward says. “We’re trying to get the broadest range so if we see changes we have that baseline.”

This data is at a regional level and has not targeted particular sites where fracking operations are taking place or are expected to do so because the BGS does not have the resources to take so many samples.

But Cuadrilla has installed groundwater monitoring wells and collected baseline data of its own covering methane, dissolved metals and a range of organic contaminants. Surface water sampling will also be done.

Ward hopes site specific company baseline data can be published alongside the BGS regional data in due course, though details have yet to be negotiated.

Casing integrity will also be important for stopping the release of methane and other gases into the atmosphere at the well head (see p14).

The Environment Agency’s draft technical guidance on fracking exploration says atmospheric monitoring must include checking for methane leaks.8 Where a site is close to an air quality management area, monitoring for nitrogen oxides produced by onsite machinery, gas flares and lorry movements may also be required (see p7).

Health concerns

But air quality monitoring for other gases is not currently listed even though these have raised major health concerns in the US. Monitoring at Fort Worth in Texas found elevated concentrations of various pollutants including carcinogenic benzene, for instance.9

Cuadrilla has signed up firm Ground Gas Solutions to do its monitoring work. Baseline figures published from its Balcombe site cover nitrogen dioxide, sulphur dioxide, hydrogen sulphide, methane, volatile organic compounds (VOCs) and the BTEX family of chemicals comprising benzene, toluene, ethylbenzene and xylenes.

Since its exploration guidance is only in draft form at present, the Environment Agency still has time to add requirements for wider air quality monitoring. Its regulatory arrangements for shale gas exploitation will also need drawing up in due course.

Its conclusion so far has been that all of the risks associated with shale gas are manageable. Indeed, it concluded that all of the potentially high-risk aspects of the process will present only a low risk once regulatory controls take effect.

The question has already been asked about whether the agency is able to regulate fracking safely, bearing in mind its funding cuts and its move towards a less interventionist approach to regulation.

Recent media articles have asked if regulators are relying too heavily on self-regulatory checks carried out by Cuadrilla.

The agency says it will use a range of methods including audits, inspections, check monitoring and sampling and record checks. It is also taking a “site specific approach” to its level of “active” monitoring. For instance, it has visited Cuadrilla’s Preese Hall site, where fracking has taken place, 16 times in the two years to June 2013. And it has visited its Grange Hall site, where exploration has yet to begin, only six times.

The Royal Society and Royal Academy of Engineering’s report also concluded that the risks associated with fracking “can be managed effectively… as long as operational best practices are implemented and enforced through regulation”.

Best practice and enforcement are key issues. But as Duke University’s Professor Jackson says: “I think if someone asks ‘can fracking be done safely’, it’s the wrong question. The question is will it be done safely?”

As the AD example shows, only time will answer that.

UK shale gas and the environment

A special report, sponsored by RPS(energy and environmental consultants)

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