Prevent groundwater pollution from underground fuel storage tanks

Assessing and preparing for risks for an underground storage tank

What you need to review before installing or using an underground storage tank for fuel.

Before you install an underground storage tank you should prepare and be able to show in writing that you:

  • have carried out an environmental risk assessment suitable to the facility
  • will have appropriate engineering requirements to prevent pollution
  • will have appropriate management systems and controls
  • have prepared emergency plans and procedures

You’ll need to consider in your review:

  • your facility’s environmental setting, in particular the vulnerability of the underlying groundwater
  • how old the facility is
  • the facility’s storage and throughput volumes (how much it processes)
  • practical engineering options and control mechanisms
  • the likely costs and benefits of upgrading the facility

Carry out a risk assessment

You should read the guide to groundwater risk assessments to see how to carry out an assessment and help you understand the source-pathway-receptor model.

For underground storage tanks (USTs) the hazard (or source) is the fuel stored (eg the liquid hydrocarbons) and handled on site. The receptor of concern is groundwater, and any surface waters or wetlands that might interact with groundwater.

The most important source-pathway-receptor interaction is the loss of product that migrates until it reaches the underlying groundwater. On reaching the groundwater, the hydrocarbons (which are classed as hazardous substances) will dissolve into the groundwater (‘dissolved phase contamination’). This is pollution and you must take all necessary measures to prevent the entry of hazardous substances to groundwater, including cleaning up any spills or leaks.

What you need to assess

It’s important you create an environmental risk assessment to make sure that you identify the risks to groundwater and the appropriate protection measures.

You should include in your written report:

  • the physical, chemical and biological properties of any material that could cause pollution
  • how you’ll store or transport materials and what the condition of the storage containers is like
  • what happens if there’s an accident, flooding, vandalism or containment failure
  • any surface water drains and foul sewers that flow off your site
  • any sustainable drainage systems you have on your site
  • whether there are areas of unsurfaced ground on the site
  • whether there are any risks because of the site’s layout and if there’s a risk of traffic collisions (eg are there any storage areas particularly at risk from cars accidently hitting them, or potential blind spots)
  • any other risks to people and the environment and the extent of the damage they could cause (eg small surface water streams running close by the site, or fuel transfer areas particularly at risk from spillages or accidents)
  • local landscape and different weather conditions and the flood risk that could be reasonably expected at and around your site

When installing a UST you need to create a more in depth assessment - see the chapter on installing a UST to see what you’ll need to assess in detail.

Create a risk management action plan

Once you’ve carried out an environmental risk assessment you should create a risk management action plan. This should set out what you’ll do to prevent groundwater pollution on your site.

When you’re preparing your action plan you should:

  • outline the engineering and operational control measures you need to protect groundwater
  • decide which risks need immediate attention and which ones you can deal with in the longer term - you may need help from your trade association or petroleum enforcement officer
  • prioritise avoiding risks over controlling them (eg consider installing tanks in less vulnerable areas before considering how to make them more secure in more vulnerable areas)

Your risk assessment will form part of the development of an environmental management system (EMS) for an operational facility. Your risk management action plan should be included as part of the EMS.

Using your risk assessment to design your facilities

You must use your findings from your risk assessment when designing new facilities or updating existing ones.

New facilities

During the risk assessment process you’ll find out the best engineering and remediation measures for environmental protection that you’ll need to be accepted at a UST facility. The Environment Agency or Natural Resources Wales (NRW) will expect you to carry out these requirements in full for a new facility.

In assessing whether engineering standards comply with the code, you should use Health and Safety Executive and industry guidance (such as the Blue Book).

See how to install a new UST for the extra information you’ll need to include in your risk assessment.

Existing facilities

With existing facilities you may not find it practical to retrofit (fit into existing equipment) in full the engineering requirements you identified in the risk assessment.

However, you should develop a plan to phase in improvements over a realistic and acceptable period agreed with your local planning authority and Environment Agency or NRW.

If you propose significant changes to an existing facility (eg installing new tanks or pipework) you’ll need to meet the requirements highlighted in the risk assessment. You’ll also need to meet any local authority planning conditions and other Environment Agency or NRW requirements, depending on the risk of the site.


You should have leak detectors installed. You must not let a situation like a leakage happen or continue because you ignored leak indication alarms. This could lead to pollution and enforcement action from the Environment Agency or NRW.

Develop an environmental management system

You need to show that you operate the facility in an environmentally responsible manner by developing operation control procedures in an environmental management system (EMS).

Your EMS should cover:

  • what measures you need to protect the environment, and how you’ll carry them out
  • how you’ll carry out checks and deal with problems
  • how you’ll carry out a management review of your environmental systems and procedures, and put in place any improvements - you may need to get professional help to develop this
  • the training processes you have in place on the site
  • your processes for dealing with emergencies (ie your pollution incident response plan)
  • any plans you have to upgrade the tank and any equipment it’s connected to
  • plans for upgrading the facility’s engineering requirements

Get EMS accreditation

If you operate a large-scale site you’ll have to get your EMS fully accredited. You’ll have to cover the cost of this yourself.

You won’t need full accreditation if you operate a small-scale site but you should still have the main components of an EMS in place. Having an accredited EMS will help show you comply with guidelines.

The two main EMS accreditation schemes are ISO 14001 and the Eco-Management and Audit Scheme (EMAS). You can also use BS 8555 - this isn’t a certifiable standard but designed to give guidance for implementing an EMS on a phase-by-phase basis.

Prepare for emergencies: create a pollution incident response plan

You should plan for any emergencies that could occur, eg major spills. You should create a pollution incident response plan (PIRP) that’s tailored to your site and sets out what you’ll do in an emergency.

Your PIRP, should include at least this information:

  • emergency contact details, eg the fire and rescue service , the Environment Agency or NRW, specialist contractors and water companies (for both water supply and foul drainage - they can be different companies)
  • an inventory of all the liquid hydrocarbons you’re storing in USTs
  • a layout plan for your site and a plan of the drainage on your site, including any discharge points
  • details of the location of emergency response equipment (eg fire extinguishers, absorbents and emergency bunding)
  • details of the location of any buried equipment, including water supply pipes
  • your processes for inspecting and looking after the site

You should create separate procedures for large-scale and small-scale incidents, including how you’ll report them.

Large-scale incidents

For a large-scale incident with a large amount of fuel lost, your PIRP may only be able to help you make sure that the immediate environmental impact is minimised rather than a full clean up.

If this happens you’ll need a longer term strategy. This will include environmental monitoring (including groundwater) and the potential use of environmental consultants to help you put your strategy in place.

Your PIRP should set out how you’ll deal with major incidents. If a leak or spill leads to significant groundwater pollution you may face:

  • substantial costs for groundwater remediation
  • additional costs associated with responding to the incident (costs may be set by the Environment Agency or NRW as part of a recovery exercise)
  • fines or costs through the criminal or civil courts
  • ongoing monitoring costs to monitor the remediation operation

In planning for large scale emergency incidents your PIRP should include procedures to:

  • prevent or minimise the spread of fuel (eg using bunding, closing the interceptor outfall)
  • prevent fire and explosion (eg isolate or switch off electrical equipment)
  • prevent further loss of product (eg uplifting fuel from a leaking tank)
  • protect the health and safety of the general public and surrounding area (eg using temporary fencing, evacuating nearby properties)
  • protect drinking water supply pipes
  • remediate (eg cleaning up pollution) and monitor groundwater as necessary

Record incidents

You should record all incidents that have the potential to damage the environment (eg fuel spills). You should consider these when updating the facility’s risk assessment.

If you make routine investigations of petrol filling sites (eg borehole logs, depth to groundwater, previous quality monitoring) you should store it centrally and make it accessible to staff and specialist contractors out of hours (eg on a central server). You should also keep records of actions you took in response to any incident.

If there’s a serious risk of fire or explosion, you should contact the fire and rescue service and police immediately.

You must also let each of the following know about any incident that leads to a significant amount of product entering the ground:

Your PIRP should explain how you’ll do the following after a major incident:

  • prevent or limit the spread of product (eg by using bunding or closing the interceptor outfall)
  • prevent fires and explosions (eg by isolating or switching off electrical equipment)
  • prevent further loss of product (eg by removing it from a leaking tank)
  • protect the health and safety of the general public and surrounding area (eg by using temporary fencing or evacuating nearby properties)
  • protect drinking water supply pipes
  • relieve the situation and monitor it
  • remove pollutants from the tank and related equipment

Where to keep your PIRP

You should keep copies of your PIRP both:

  • on-site
  • at off-site locations where they can be easily accessed

You should list all people or organisations that have the PIRP and you should keep it up to date. You should re-issue the PIRP if there are any changes in the retained contractors.

You may also want to provide copies to:

  • the fire and rescue service
  • the Environment Agency or NRW
  • other regulatory authorities
  • specialist contractors working on your site

You should keep an up-to-date record of everyone who has a copy of your PIRP.