Prevent groundwater pollution from underground fuel storage tanks

Using an underground storage tank

How to use an underground storage tank safely to minimise the risk to groundwater.

Leaks can happen when you move fuel to and from your storage facilities. You should develop operation control measures to prevent spills or leaks:

  • during the delivery of liquid hydrocarbon product to your tank
  • during storage
  • when you’re dispensing fuel (eg when customers fill up their car)
  • when you’re removing waste from the site through drains
  • during maintenance and repairs

The level of risk to groundwater will depend on your engineering and operational control measures and on the facility’s location.

Make sure product is delivered safely

Spills can happen during the delivery of fuel to a tank, eg:

  • during the uncoupling of delivery pipes
  • due to split hoses or leaks from offset fill pipes

As part of your environmental risk assessment before installing your tank you should have considered the risks to groundwater during delivery. To protect groundwater during delivery, you should make sure:

  • the site has a separate tanker stand area
  • the site’s drainage system can capture spills from the delivery point
  • the interceptor has enough capacity and has been regularly maintained
  • there are overfill prevention systems on the site
  • delivery pipes are clearly labelled
  • that the correct delivery procedures are being followed

Store product safely

You could lose a significant amount of product if tanks and pipes fail during storage. As part of your environmental risk assessment before installing your tank you should have considered the risks to groundwater during storage.

When you’re carrying out an environmental risk assessment of existing equipment you should consider:

  • the age of the tank and pipes - older tanks are likely to be single-skinned and made from steel and so be a greater risk
  • how close the base of the tank is to groundwater
  • the type of ground the tank is installed in - eg loose ground may affect the tank’s long-term stability, or the ground could react with the tank
  • whether the tank and pipes are single or double-skinned and the materials they’re made from - single-skinned tanks are a greater risk
  • how the tank and pipes were installed
  • whether the tank and pipes are damaged
  • whether the tank and pipes have received corrosion protection (eg cathodic protection)
  • whether interstitial and wetstock monitoring is functioning correctly

Avoid spills and leaks during dispensing

You should make sure product doesn’t spill or leak:

  • from the pipes connecting the tank to the dispensing system
  • during the dispensing process

You should take extra care in situations where spills are likely to discharge into the water environment, eg during the refuelling of boats. In these situations you should be aware of the immediate impact any spills will cause and make sure you’ve covered this in your risk assessment.

When you’re carrying out an environmental risk assessment of existing equipment you should consider whether dispensers:

  • conform to modern standards as set out in the Blue Book
  • are fed by a suction or a pressure system
  • are regularly calibrated and serviced
  • are fitted with nozzle shut-off valves

See the the Blue Book for further details on what to consider and why.

Your risk assessment should also identify whether:

  • you can refuel vehicles on the site
  • pumps on the suction system are fitted with under-pump check valves
  • the site is secure against damage or vandalism

Make sure drainage system is working properly

Your drainage system should be designed to carry all contaminated water and spills to collection or containment points for disposal or treatment. You must deal with contaminated run-off legally - eg discharging to foul sewage under a trade effluent agreement with your waste carrier, or collecting and paying for it to be tankered away.

If you’re using a petrol interceptor, you should make sure it discharges to a foul sewer - you’ll need to get approval for this from your sewerage undertaker.

When you’re carrying out an environmental risk assessment you should consider:

  • whether the drainage system is intact and can deal effectively with fuel spills
  • whether the drainage system covers the whole site
  • the age and condition of the drainage system
  • the links between drainage system and the water environment (eg groundwater, lakes and rivers), particularly if you’re in a sensitive environment, like close to a wetland or in a source protection zone or in an area at risk from flooding

Your risk assessment should also cover:

  • the environmental sensitivity of the underlying aquifer and how vulnerable it is to pollution
  • whether waste materials or effluents are discharged from the site
  • whether there are any soakaways on the site (and whether they should be decommissioned)
  • the distance of the nearest water supply boreholes (both public and private)
  • whether the forecourt oil or water separator is clean and functional, and where it discharges to
  • whether there are good dispensing and monitoring procedures in place on the site
  • whether any vehicle washing facilities drain through a separate dedicated system

Deal with effluent and run-off from vehicle washing and cleaning activities

If you cause pollution you’re breaking the law. Pollutants that you need to deal with include things that are washed off, like:

  • hydrocarbon residues (from spillages)
  • dirt
  • brake dust
  • traffic film residue
  • oil

Your cleaning agents (including those labelled biodegradable or traffic film removers) are also pollutants.

Trade effluent is dirty water or run-off from vehicle washing and cleaning carried out as a business or industrial activity. You must arrange for collection and disposal of effluent to prevent pollution. It’s illegal to discharge trade effluent to the environment or into drains without permission from your local sewage undertaker.

In particular you should make sure cleaning effluent, run-off or cleaning chemicals don’t enter:

  • oil separators
  • drains or gullies connected to the surface water drainage system

You need to have an up-to-date plan of your whole site that identifies where vehicle washing and cleaning takes place. This will help you to make sure drains are connected to the right system. Use a drainage consultant or consulting engineering company to create this plan if you can’t do it in-house.

Your risk assessment should also consider how you’ll prevent spills or leaks during repairs, including how you’ll:

  • first drain the pipeline and tanks
  • avoid accidental damage to tanks and pipes
  • make sure you have any materials needed to deal with small spills (eg absorbent granules, mats)
  • carry out monitoring and checks to make sure repairs are done properly
  • discharge any materials (including waste waters) containing waste fuels lawfully (eg to a permitted waste disposal site)

Operation, leak detection and maintenance

The design and engineering of your operational control systems should help reduce risks to groundwater. For example, making sure you adopt best engineering standards. Appropriate leak detection systems will help reduce the risk of groundwater pollution.

You should also have an appropriate operational control system, a system including procedures that the operator has explaining how they will run their activity and in a way that minimises the risk of pollution. Your operational control system forms part of the EMS and should include:

  • general operational control procedures
  • leak detection and environmental monitoring
  • maintenance

These should form part of your facility’s environmental management system (EMS).

Your measures to reduce risks to groundwater will share features with your fire control measures (eg bunding arrangements to contain fire fighting waters) - you need to make sure that there is full integration between the 2 systems. You can get more information in the Blue Book.

Correct operational procedures form a major part of risk mitigation and help reduce the risk of pollution occurring and damage caused from an incident.

Significant activities you should have developed operational control procedures for include:

  • product delivery
  • fuel dispensing
  • product volume monitoring
  • regular and one-off maintenance activities
  • how to control visiting contractors
  • staff awareness and training
  • how you’ll respond to major and minor spillages
  • how you’ll respond to alarms and other signs of leakage

Detecting leaks

You should detect leaks through (in order of priority):

  • automatic leak detection systems
  • wetstock monitoring
  • environmental monitoring
  • integrity testing

If your tank is in an environmentally sensitive area, your leak detection system should detect leaks immediately, before the surrounding area is seriously affected.

As part of your environmental risk assessment you should identify the minimum detectable leak that your detection system can identify. Find out more about monitoring and testing tanks and related equipment in the Blue Book and PETEL 65/34.


You should have a regular maintenance and inspection programme to keep everything in good working order and to demonstrate that you’re managing the environmental risk.

You need to have these procedures as part of an EMS and through ISO 14001.

You must follow a plan of works when carrying out any maintenance or repair work on an underground storage tank or associated pipework.

Keep records

You should keep records relating to your tank and any equipment connected to it. Your fire and rescue service, the Environment Agency or Natural Resources Wales (NRW) may ask to see your records if there’s an incident or if your site’s inspected.

These will help when you’re:

  • doing further building work on the site
  • decommissioning or removing equipment

Records should include technical drawings. These should show:

  • the location and orientation of the tanks and pipes
  • their dimensions
  • the materials used

You should also:

  • record all repairs and alterations to the system
  • keep records dated and maintained during the life of the tank
  • keep records on the site for future reference (eg in the event of a leak or spillage)