Onshore oil and gas sector guidance

5. Groundwater activity or water discharge activity permits

Groundwater activity and water discharge activity permits for onshore oil and gas sites, groundwater exclusions, and protecting groundwater sources.

5.1 When you need a groundwater activity permit

Groundwater is all water underground in the saturated zone (below the water table) and in direct contact with the ground or subsoil. Deep geological formations that are sufficiently porous and permeable are likely to contain groundwater. The Environment Agency would normally consider that shales do not contain groundwater.

You need a groundwater activity permit if:

  • you discharge surface water run-off from your site (which may contain pollutants) into the groundwater environment such as a soakaway
  • you are re-injecting produced water on the site
  • you are proposing to carry out hydraulic fracturing for onshore oil and gas and there is a risk that pollutants might enter groundwater as a result of injecting fracturing fluid

Read section 11 ‘Produced water and flowback fluid: re-injection and reuse’ for more information about re-injection.

5.2 Groundwater exclusions

Some activities may not need a permit and are covered by a ‘de minimis’ exclusion because the volume of discharge is low and it has a minimal pollutant concentration. This guidance about groundwater exclusions explains what is meant by a de minimis exclusion.

The Environment Agency expects the following onshore oil and gas activities will be covered by a de minimis exclusion. But they will review all activities on a case by case basis to make a decision:

  • using additives assessed as non-polluting to groundwater in drilling fluids - including oil-based muds
  • borehole acidisation – providing the acids you use are not regarded as waste – if they are you need a mining waste permit
  • leak off tests – as this is a small scale test using low volumes of water
  • acid wash – as the dilute acid used will be quickly neutralised as it reacts with the drilling fluid and the geological formation

5.3 Groundwater, source protection zones and oil and gas activities

Groundwater that is important for drinking water supplies or sustains rivers, lakes and wetlands must be protected. Source protection zones (SPZs) are an important tool for protecting sources used for drinking water or food production.

The Environment Agency will not allow drilling for oil and gas in a SPZ 1. This includes SPZ 1 areas where the aquifer is at the surface, and SPZ 1c sub-surface areas, where the aquifer is confined.

If the Environment Agency thinks there may be a risk to groundwater, they will not allow drilling for oil and gas in other areas – such as SPZ 2, SPZ 3 or entirely outside of a SPZ.

Under the Petroleum Act 1998, the minimum depth at which you can carry out high volume (associated) hydraulic fracturing is 1,000m below the surface. In a SPZ 1, the minimum depth is 1,200m below the surface.

The Environment Agency will allow hydraulic fracturing under a SPZ, provided you:

  • follow the depth restrictions
  • can demonstrate that the risks to groundwater are low

For conventional oil and gas activities that are not covered under the Petroleum Act, there is not a set minimum separation distance between the target formation and the surface. The Environment Agency will assess whether the distance is acceptable on a case by case basis.

In all cases, the Environment Agency will also look at the distance between your activities and the nearest aquifer – the vertical, horizontal and inclined distance.

5.4 Groundwater risk assessments

You must submit a groundwater (hydrogeological) risk assessment with your application for a groundwater activity permit.

The guidance Groundwater risk assessment for your environmental permit provides generic information on how to develop a conceptual model and carry out a hydrogeological risk assessment.

For onshore oil and gas activities, your risk assessment should evaluate any risks to groundwater and associated receptors from:

  • substances used or released from activities on the surface such as additives to drilling and fracturing fluids
  • hydrocarbons and other substances released from depth, for example methane, metals, salts and naturally occurring radioactive materials
  • drilling the well – this may release particles of rock causing increased turbidity in the groundwater
  • any well stimulation or down hole activities – including hydraulic fracturing

Your groundwater risk assessment also needs to provide information about the following.

How you will construct your site to protect groundwater

You need to provide information on how you will construct the site to protect the underlying ground and groundwater – for example through:

  • impermeable liners
  • managing surface run-off
  • surface water drainage, treatment and containment
  • secondary and tertiary containment measures
  • the design and installation of the drilling platform

You will also need to include information about:

  • your method of well cellar and well construction
  • casing and grouting proposals for the full depth of the borehole
  • how and when you will test the integrity of the casing

If the Environment Agency grants your permit, they may include conditions covering site construction. These could include:

  • installing an impermeable liner across the site before you start any drilling operations - see section 7.8 about best available techniques for managing extractive waste
  • installing locking valves on all surface water drains to securely isolate the site drainage system
  • providing bunding around containers storing materials that may cause pollution
  • cleaning and washing down all equipment in a suitably bunded area and having measures in place to dispose of wash down waters

Read the Construction Industry Research and Information Association (CIRIA) report Containment systems for the prevention of pollution (C736) to find out about standards for secondary and tertiary containment.

Safeguards you will put in place to prevent pollution

You will also need to provide details of the safeguards you will use to prevent the cross-contamination of aquifers and water ingress. For example, through effectively installing and cementing casings in place:

  • during drilling
  • during subsequent operations
  • following decommissioning of the well

You also need to provide details of:

  • the safeguards you will use to prevent uncontrolled loss of fluids (including gaseous losses) in the borehole to formations, or ground, from the surface (blowouts)
  • restoration measures you will use if a loss of containment occurs

Substances you will use

Your risk assessment must provide details of all the chemicals you will use for drilling and down hole activities – including well stimulations and hydraulic fracturing activities.

You need to provide details of each substance you propose to use, including:

  • the maximum quantities and composition of all fluids
  • for hydraulic fracturing activities, details of substances used to prop open fissures and how the process will be monitored
  • an estimate of the quantity of injected fluids that will remain underground
  • the composition and function of drilling fluids and any stimulation or well treatment fluid you will use for each section of the drilling programme – including a material safety data sheet for each fluid

You do not need to list the exact chemical composition (individual chemicals and precise proportions) of the commercial products you are using. However, you must disclose information about the chemicals you will use in total and the maximum amount of each chemical.

This includes disclosing information on discharges of chemicals which are subject to the ‘de minimis’ exclusion. These are discharges that are of low volume and that have minimal pollutant concentration. This information allows us to consider their potential environmental impact.

You must not use hazardous substances for drilling or hydraulic fracturing. You may use other substances providing they do not pollute groundwater. If you’re applying for a Hydraulic Fracture Consent you need to show the Department for Business, Energy and Industrial Strategy (BEIS) that the Environment Agency has approved the substances you want to use.

For principal and secondary aquifers for which groundwater bodies are defined under the Water Framework Directive, you can use air flush, water only or water-based fluids.

Acceptable additives for water-based fluids are:

  • bentonite
  • food grade thickeners such as xanthan or guar gums
  • inert materials to increase density such as barite (barium sulphate) or haematite (iron oxide)

In karstic or highly fissured conditions, you must only use inert materials.

In deeper, saline aquifers, or deep formations, you may use water-based muds with a wider range of additives and oil-based muds. However, these must not cause pollution to groundwater.

The Environment Agency will assess whether they can approve the substances you propose to use. To identify hazardous substances, they will use the published assessment methodology on the Water Framework Directive UK TAG website.

Operators can also follow the Joint Agencies Groundwater Directive Advisory Group (JAGDAG) methodology and submit an assessment of the chemicals they propose to use to the Environment Agency for review.

A list of all of the substances which have been reviewed and assessed as hazardous, following public consultation, can be found on the Water Framework Directive UK TAG website.

Water use and effluent disposal

Your risk assessment also needs to provide information about your proposed water use and how you will dispose of effluents.

5.5 When you need a water discharge activity permit

You need a water discharge activity permit if you discharge surface water run-off from your site into a watercourse, such as a stream or river. The surface water run-off may contain pollutants from your site.

You must manage any surface water run-off from your site and prevent any uncontrolled, polluting discharges.

Surface water run-off should be stored in an engineered collection and management system. This system may need to include treatment to make sure any discharged water is not contaminated.

You can apply for a permit to discharge uncontaminated water into a watercourse as a surface water discharge activity.

If this is not an option, then you could apply for a permit to discharge to a soakaway – as a groundwater activity. However, you can only do this if:

  • the ground conditions are appropriate
  • you can demonstrate that the risk to underlying groundwater is acceptable
  • the land beneath the site is not contaminated – the discharge could mobilise underground pollutants that may be trapped in the geology and cause pollution

If you are not able to discharge surface water run-off from your site using these options, you will need to arrange for the water to be collected for disposal at an appropriate facility.

If you want to re-inject surface water run-off, read section 11 about Produced water and flowback fluid: re-injection and reuse.

5.6 Surface water discharge risk assessment

If your activity discharges treated sewage or trade effluent into surface water you will need to do one or both of the following risk assessments and submit with your permit application: