Slurry and silage storage compliance (SSAFO)

What SSAFO covers

The regulations apply to three types of storage:

Silage

Any crop being made into silage or silage being stored, including:

• Silage clamps and silos
• Silage effluent (the liquid that drains from silage)
• Baled silage stored in fields

Slurry

Liquid or semi-liquid matter composed of:

• Excreta produced by livestock while in a yard or building (including wood chip corrals)
• Mixtures of livestock excreta, bedding, rainwater, and washings that can be pumped or discharged by gravity

Agricultural fuel oil

Oil intended for use as fuel for heat or power on the farm. This does NOT include:

• Oil stored exclusively for heating a farmhouse or other residential premises (if stored separately)
• Oil in transport tankers

Who must comply

SSAFO applies to anyone with custody or control of silage, slurry, or agricultural fuel oil on a farm. This includes:

• Farmers storing silage in silos or clamps
• Farmers storing slurry from housed livestock
• Farms storing more than 1,500 litres of agricultural fuel oil
• Contractors storing these materials on agricultural premises

Key distances and construction standards

All new, substantially enlarged, or substantially reconstructed storage must meet these requirements:

Slurry storage requirements

Slurry storage systems must be constructed to prevent any risk of pollution to water. This section covers capacity requirements, construction standards, and freeboard rules.

Minimum storage capacity

Your slurry store must hold the maximum quantity of slurry likely to be produced in any continuous period when you cannot spread. The minimum requirements are:

Construction standards

All slurry storage systems must be:

• Impermeable: Base of storage tank, base and walls of effluent tank, channels, reception pit, and walls of pipes must be impermeable
• Corrosion protected: Protected against corrosion in accordance with BS 5502:Part 50:1993
• Structurally sound: Base and walls must withstand characteristic loads per BS 5502:Part 50:1993

Freeboard requirements

Freeboard is the distance between the slurry surface and the top of the store. You must maintain minimum freeboard during use:

Reception pits

Reception pits collect slurry before transfer to main storage. They must hold the maximum slurry likely to be produced in any 2-day period, including likely rainfall. Maintain 300mm freeboard in reception pits.

Drainage valves

If your store has a drainage pipe, it must have:

• Two valves in series, separated by at least 1 metre
• Each valve capable of shutting off flow completely
• Both valves kept shut and locked when not in use

This requirement does not apply if the pipe drains to another tank at the same level or of equal or greater capacity.

Earth-banked stores (weeping wall and lagoons)

If storing slurry above the natural level of adjoining land with walls constructed of earth:

• Must have an impermeable lining
• Minimum 750mm freeboard
• Must be designed so walls do not leak even if the lining is punctured

Silage storage requirements

Silage silos and clamps must be constructed to contain silage effluent, which is highly polluting if it reaches watercourses.

Silo base construction

The base of a silo must:

• Extend beyond any walls of the silo
• Have effluent collection channels draining to an effluent tank
• Be designed to BS 8007:1987 (concrete) or BS 5502:Part 21:1990 (hot-rolled asphalt)
• Be impermeable and resistant to attack by silage effluent

Effluent tank capacity

The effluent tank must provide at least 2 days storage at peak flow. Minimum capacity depends on silo size:

Example calculation: A 2,000 cubic metre silo requires: 30 + (500 x 0.0067) = 33.35 cubic metres minimum effluent tank capacity.

Baled silage

Baled silage sealed in impermeable membrane or bag does not need a specially constructed base. However:

• It must not leak into water sources
• It must be kept at least 10 metres from inland or coastal waters
• You must not open silage bales within 10 metres of water (this is a criminal offence)

Fuel oil storage

SSAFO requirements apply when the total quantity of agricultural fuel oil stored on your farm exceeds 1,500 litres. This includes oil in single tanks, multiple tanks, or drums across the farm.

Construction standards

The bund and base must be:

• Impermeable to water and oil
• Strong enough to remain impermeable for at least 20 years with proper maintenance

Tank positioning and controls

• Every part of any fuel storage tank must be within the bund
• Taps and valves must be within the bund and directed downward into it
• All taps and valves must be locked shut when not in use
• The bund must not contain any outlet or drain

Notifying the Environment Agency

You must notify the Environment Agency before constructing new storage or making substantial changes to existing storage.

When notification is required

• Building a new silo, slurry storage system, or fuel oil store
• Substantially enlarging an existing store
• Substantially reconstructing an existing store
• Using a new field site for silage storage

"Substantial changes" means structural alterations, not minor repairs. If you are unsure whether your planned work requires notification, contact the Environment Agency.

Notification process

What to include in your notification

• Type of silo or storage system (slurry tank, silage clamp, fuel oil store)
• Location on farm (grid reference if possible)
• Site plan showing water features, drains, and distances
• Design drawing with materials specification
• Manufacturer specifications for prefabricated products
• For earth-banked stores: soil analysis
• For underground silage effluent tanks: installer certification

Penalty for failing to notify

Failing to notify the Environment Agency before construction is a criminal offence punishable by a fine. This is separate from any penalties for non-compliant construction.

Exemptions

Certain structures are exempt from SSAFO construction requirements, though they may still be subject to enforcement if they cause pollution.

Pre-March 1991 structures

SSAFO regulations do NOT apply to silos, slurry storage systems, or fuel storage tanks:

• Used before 1 March 1991 for making silage, storing slurry, or storing fuel oil
• Constructed before 1 March 1991 for such use (even if not yet used)
• Where the contract for construction was entered into before 1 March 1991 and work completed before 1 September 1991

Other exemptions

• Temporary storage in transport: Agricultural fuel oil stored temporarily in a tanker for transport on roads or around the farm
• Domestic heating oil: Oil intended exclusively for heating a farmhouse or other residential premises, if stored separately from other oil
• Small fuel oil quantities: Farms storing 1,500 litres or less of agricultural fuel oil (EA recommends following Code of Good Agricultural Practice even if exempt)

Inspections and enforcement

The Environment Agency conducts farm inspections to check SSAFO compliance. They can visit without prior notice.

Inspection triggers

Inspections may be triggered by:

• Routine compliance checks
• Pollution incidents or reports
• Agri-environment scheme checks (for farms receiving government payments)
• Neighbour complaints
• Follow-up to previous enforcement action

Common non-compliance issues

The Environment Agency's 2024-25 inspections found high rates of non-compliance:

Enforcement powers

The Environment Agency has several enforcement options:

Regulation 7 notice

If your storage poses a significant pollution risk, the EA can serve a notice requiring works or precautions to reduce the risk. The notice specifies what works are required and the compliance period. You can appeal to the Secretary of State within 28 days.

Civil sanctions

• Compliance notice: Requires specific actions to achieve compliance
• Restoration notice: Requires steps to restore the environment to its pre-offence state
• Fixed monetary penalty: Standard penalty for specified offences
• Variable monetary penalty: Penalty proportionate to offence severity
• Stop notice: Prohibits continuation of activity causing harm
• Enforcement undertaking: Voluntary agreement to take remedial action

Criminal prosecution

SSAFO offences can be prosecuted as criminal offences:

Penalties are unlimited fines in both magistrates' and Crown courts. Pollution incidents can also result in imprisonment.

Offences include:

• Contravention of silage storage requirements
• Contravention of slurry storage requirements
• Contravention of fuel oil storage requirements
• Opening silage bales within 10 metres of water
• Failing to comply with a Regulation 7 notice

Incident reporting

Any pollution incident must be reported to the Environment Agency immediately via the 24-hour hotline: 0800 80 70 60.

Funding for storage improvements

If you need to build or expand slurry storage to meet SSAFO or NVZ requirements, grant funding may be available.

Planning considerations

New slurry stores may require planning permission from your local authority. Check with your local planning department before starting any major infrastructure project. The Slurry Infrastructure Grant includes guidance for working with planning authorities.

Next steps

1. Assess your current storage: Calculate whether you have sufficient capacity for 4 months (non-NVZ) or 5-6 months (NVZ) using the AHDB Slurry Wizard
2. Check construction standards: Inspect stores for cracks, damage, or non-compliant features (missing valves, inadequate freeboard)
3. Determine NVZ status: Use the GOV.UK interactive map to check if your land is in a Nitrate Vulnerable Zone
4. Plan any upgrades: If storage is inadequate, investigate Slurry Infrastructure Grant funding before planning works
5. Notify the EA: Submit notification at least 14 days before any construction or substantial modification
6. Maintain records: Keep construction records, maintenance logs, and any EA correspondence