Storing silage, slurry and agricultural fuel oil
Rules you must follow, who’s responsible, when to tell the Environment Agency and what to do if you get an enforcement notice.
Applies to England
You must follow these rules if you store silage, slurry or agricultural fuel oil.
You need to know the general rules that apply if you store any of the 3 substances, as well as specific rules for storing and handling each one.
If your farm is in a nitrate vulnerable zone (NVZ) there are extra rules for storing organic manures. You can check if your farm is in an NVZ.
General rules
Who’s responsible
You must make sure you meet the rules if you’re a:
- farmer
- land manager
- tenant farmer – unless you can prove someone else, for example the leaseholder, is jointly or wholly responsible
If you do not follow the rules or take care to avoid causing pollution you can be prosecuted and fined up to £5,000 in a magistrates’ court, or get an unlimited fine in the Crown Court.
New storage and substantial changes
A new or substantially changed store must:
- follow the specific rules for the substance you’re storing
- have an expected lifespan of at least 20 years with maintenance – any part of a silage effluent tank that’s underground must last 20 years without maintenance
- be at least 10 metres clear of inland or coastal waters – you may need a larger safety zone in some cases, for example near a water supply intake
Although your store itself must be at least 10 metres clear of inland or coastal waters, drains and sealed pipes can be within 10 metres of these features if the Environment Agency agrees an exception. Ask for an exception when you tell the Environment Agency about your project.
Substantial changes usually means structural alterations, rather than minor repairs. Check with the Environment Agency if you’re not sure.
Exempt storage
If your installation was built before March 1991, or a contract for construction was entered into before March 1991 and completed before September 1991, it’s exempt from the rules for new stores. However, if you make substantial changes, for example structural changes, increasing capacity or relocating your store, it is no longer exempt.
The Environment Agency can also serve a notice at any time requiring you to bring storage up to the current standards if it believes there’s a significant risk of pollution.
Before you start work
It’s up to you to decide what planning and work is needed but you must:
- tell the Environment Agency at least 14 days before you begin construction – you can also contact them for advice on planning and building a store
- make sure you do not pollute the surrounding environment – for example rivers or other watercourses
- check if you also need planning permission
Once your storage is built you must carry out maintenance to make sure there’s no risk of pollution.
Tell the Environment Agency
You must tell the Environment Agency at least 14 days before you build new storage for silage, slurry or agricultural fuel oil, or make substantial changes to an existing store.
You must also tell the Environment Agency if you intend to make or store field silage or non-baled bags – there are specific rules and a form.
Contact your local office
Call or write to your local Environment Agency office.
Tell them:
- your name, address, telephone number and email address
- the type of store you’re proposing to build or change
- the exact location of the site (8-figure grid reference)
For the Environment Agency to assess your proposal you’ll need to supply:
- a site plan drawing of the structure
- a design drawing confirming the materials that will be used and their design, specification and layout – you may also be asked to confirm that your design meets the requirements of BS 5502
- if you plan to use prefabricated products, a copy of the manufacturer’s specifications and guarantee
- if the structure is constructed from earth, analysis about the soil type, depth and permeability and a description of how it will be engineered
- for underground or partially underground silage effluent tanks you’ll need a certification from the installer – you must provide this certification to the Environment Agency because the tank is required to perform for at least 20 years without maintenance
You’ll usually get a written assessment of your proposal that says whether it’s been approved or not. The Environment Agency may contact you, rather than giving you a written assessment, to give you guidance on changes you need to make to your installation before it can be approved.
Rules for making and storing silage
The rules do not apply to silage you store temporarily in a container or trailer for transportation.
Where to store silage
You must not make or store any silage, or unwrap baled silage within 10 metres of inland or coastal waters.
In addition, you must not store field silage within 50 metres of a protected water supply source. This is any place where water is abstracted (taken) for any of the following purposes:
- human consumption
- use in farm dairies
- human food preparation
Ask the Environment Agency about protected water sources or use Magic map to check your local area.
Silos
All parts of a silo must be resistant to attack.
Your silo must have:
- an impermeable base extending beyond any walls
- impermeable drainage collection channels around the outside, flowing into an effluent tank
The base must comply with:
- British Standard 8007:1987 and British Standard 8110-1:1997 (for concrete bases)
- British Standard 594/EN 13108-4:2006 (for hot-rolled asphalt bases)
If your silo has walls, they must withstand wall loadings set in British Standard 5502-22:2003+A1:2013.
Ask your manufacturer, or check the manual that came with your equipment, to find out if it meets these British Standards.
Effluent tanks
Your silo must have an effluent collection system.
If all parts of an effluent tank are above ground the tank must be constructed to resist attack from silage effluent for at least 20 years with maintenance. If any part is below ground it should be impermeable for at least 20 years without maintenance. You’ll be asked to prove your tank is suitable, for example with a manufacturer’s guarantee.
You can store silage effluent and slurry together if your tank has enough capacity and is built to withstand both types of effluent. However, mixing slurry can give off gases that are lethal to humans and livestock and you must never put silage effluent into an under-floor slurry store.
Capacity
The minimum capacity rules for effluent tanks should give you at least 2 days’ storage at peak flow. However, it’s up to you to make sure you’ve got enough capacity to avoid the risk of pollution.
| Silo capacity | Minimum effluent tank capacity |
|---|---|
| Up to 1,500 cubic metres | 20 litres for each cubic metre |
| Over 1,500 cubic metres | 30 cubic metres, plus 6.7 litres for each cubic metre of silo capacity over 1,500 cubic metres |
Store baled silage
You must seal baled silage in an impermeable membrane or bag. It does not need a specially constructed base but you must make sure any silage stored directly on the ground cannot leak into a water source.
You must keep baled silage at least 10 metres clear of inland or coastal waters.
Field silage and non-baled bags
For silage to be stored as field silage there must be no construction works, for example walls or earth banks. Also, topsoil must not be disturbed.
If you make field silage or non-baled bags, you must:
- choose a suitable site – for example if you store silage in a non-baled bag in your farmyard, you must make sure you can contain any drainage
- tell your local Environment Agency office at least 14 days before you first use the site
Use form WQE4 to tell the Environment Agency if you intend to make or store field silage. Give at least 14 days’ notice. Send the completed form to your local Environment Office.
Rules for making and storing slurry, including in earth-banked stores
Slurry is run-off from:
- solid manure stores
- woodchip
- straw-bedded corrals
- stand-off pads
You must collect and store it either separately or in your main slurry store. This does not apply to slurry you store temporarily in a container or trailer for transportation.
If you use a slurry separator you need to store and spread the separated liquid and more solid organic manure correctly. Follow the guidance on using a mechanical slurry separator to manage your slurry.
Where to store slurry
You must not put slurry storage tanks, effluent tanks, channels or reception pits within 10 metres of inland or coastal waters without written agreement from the Environment Agency.
All slurry stores
Slurry tanks, reception pits, pipes and channels must be impermeable and meet the anti-corrosion standards set in British Standard 5502-50:1993+A2:2010. They should last for at least 20 years with maintenance.
The base and walls of your slurry tank and any reception pit must withstand the wall loadings set in the standard.
You’re responsible for making sure your storage and maintenance complies with the rules – get professional advice if you need it.
Capacity
Freeboard is the vertical distance between the crest of your tank or lagoon and the slurry surface.
When you calculate the required capacity of your steel or concrete store, you’ll need to include a minimum of 300 millimetres of freeboard. For earth-banked stores you’ll need a minimum of 750 millimetres and you must maintain this freeboard during use. You’ll normally need capacity for at least 4 months’ slurry storage. What this means for you will depend on how much slurry you use, the size of your tanks and expected rainfall.
Use MANNER NPK to work out your average winter rainfall November to February. Add an extra 25% to your calculation to take account of wetter than average winters.
If you’re in an area with above average rainfall you’ll need more capacity. Speak to the Environment Agency or a consultant if you’re not sure how much you’ll need.
If you operate with less than 4 months’ capacity, the Environment Agency may refuse your proposal or ask you to prove that it’s sufficient and to explain the steps you’ve taken to protect the environment.
Any temporary storage facilities you have – such as a reception pit – must be large enough to store a minimum of 2 days’ combined slurry production and likely rainfall.
Drainage pipes
If your slurry tank, effluent tank or reception pit is fitted with a drainage pipe it must have 2 valves separated by a least 1 metre. Each valve must be able to shut off the flow of slurry and be locked when not in use.
This rule does not apply if your slurry storage tank drains through the pipe into another tank at the same level, or of equal or greater capacity.
Earth-banked slurry stores
An earth-banked store must have impermeable soil to a thickness of at least 1 metre. You may need laboratory analysis and confirmation from a civil engineer to be sure your soil is suitable. Alternatively, you can import impermeable soil or use a synthetic liner.
The permeability of your compacted soil must be less than 1 x 10-9 metres per second (0.000001 mm per second). Testing should be to BS 1377-6:1990 or to BS EN 1997-2:2007.
Weeping-wall stores
The base of a weeping-wall store must extend beyond its walls and include perimeter drains to catch escaped slurry and drain into an effluent tank.
Spreading slurry
Your irrigation system must not deposit slurry within 10 metres of inland freshwater or 50 metres of any water supply. You must assess the risk of direct run-off from land you intend to irrigate, and identify unsuitable areas.
Agricultural fuel oil
You must follow these rules if you both:
- build a new agricultural fuel oil store or make substantial changes to an existing one
- store over 1,500 litres of agricultural fuel oil on your farm
Other rules may apply if you store fuel oil:
- for domestic purposes
- for another business you run from your farm
- in a tanker temporarily for transportation on roads or around your farm
- in mobile bowsers or drums temporarily stored alongside mobile plant
Wherever fuel oil is stored on your land you’re responsible for taking precautions to prevent and contain spillages – for example by fitting an alarm to alert you to overfilling.
Where to store fuel oil
You can store fuel oil in one location or spread across your farm. It must be stored in a tank or drum that meets ISO 9000. You should check the manual that came with your tank or drum, or ask the manufacturer.
No part of your installation can be within 10 metres of inland or coastal waters – including yard drains, dry ditches and land drains.
If tanks are underground, they must also follow the Department for Environment, Food & Rural Affairs (Defra) groundwater protection code.
Secondary containment
A tank or drum must be surrounded by a secondary containment structure or bund.
The bund must:
- have a life expectancy of at least 20 years with maintenance
- be impermeable to oil and water (walls and base), with no drain-down pipe
- contain every part of the tank, with taps and valves directed down and locked shut when not in use
- contain delivery pipes that are permanently attached to the primary tank, which must be fitted with self-closing taps or valves and locked inside when not in use
If you buy a combined storage tank and bund system you must make sure it will meet the regulations when in use.
You must dispose of any waste fuel oil or mix of oil and water that collects in the bund without causing pollution.
Bund capacity
The required capacity of a bund depends on your type of storage.
| Type of storage | Minimum capacity of bund |
|---|---|
| Single tank | 110% capacity of the tank |
| Multiple tanks | 110% of the capacity of the largest tank or 25% of the total volume that could be stored in all tanks in the area – whichever is greater |
| Other storage – for example, drum | At least 25% of the total volume that could be stored at any time |
If you’re served a notice
The Environment Agency can serve a notice to stop you using an unsuitable silage, slurry or agricultural fuel oil store until it’s improved or relocated. They’ll do this if they think there’s a significant risk of pollution – for example if you’ve not allowed enough capacity to store slurry.
You’ll have at least 28 days to carry out the work. You may be allowed more time, for example if you need planning permission or the weather is unsuitable.
How to appeal
If you disagree with the notice, you can appeal. You have 28 days from the day after the notice was served.
Appeal in writing to the Secretary of State.
The Secretary of State for the Environment and Rural Affairs
The Planning Inspectorate
Room 4/19 Eagle Wing
Temple Quay House
2, The Square
Temple Quay
Bristol
BS1 6PN
Send a copy to your Environment Agency office at the address on the notice.
Your letter must explain why you’re appealing.
You should include:
- a copy of the notice
- any related correspondence
- a plan of your farm, showing the installation and any watercourses or drains
If you’re acting for a farmer who was served the notice, you’ll also need a statement from them to confirm this.
Decisions on appeals
The notice could be:
- withdrawn or changed
- upheld, with extra time for you to comply
- upheld, with no extra time to comply – the compliance period will then usually end on the day this decision is made
Legislation
These rules are based on the Water Resources (Control of Pollution) (Silage, Slurry and Agricultural Fuel Oil) (England) Regulations – known as the SSAFO regulations – and related legislation.
Updates to this page
Last updated 12 October 2023 + show all updates
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Added a link to guidance on using a mechanical slurry separator to manage your slurry.
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Link to PLANET replaced with one to MANNER NPK software.
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Amended to explain extra 25% should be added to calculations of average winter rainfall.
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Amended standards for compacted soil permeability.
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First published.