Guide
Slurry and silage storage compliance (SSAFO)
How to comply with SSAFO regulations for storing silage, slurry, and agricultural fuel oil on farms. Covers construction standards, storage capacity requirements, notification procedures, exemptions for pre-1991 structures, and Environment Agency enforcement. Includes guidance for farms in Nitrate Vulnerable Zones where stricter storage requirements apply.
The SSAFO Regulations set construction and maintenance standards for silage, slurry, and agricultural fuel oil storage to prevent water pollution. They apply to all farms in England that store these materials.
SSAFO stands for Silage, Slurry, and Agricultural Fuel Oil. The regulations came into force in 2010 and are enforced by the Environment Agency. Failure to comply is a criminal offence carrying unlimited fines.
Environment Agency inspections found 51% of farms non-compliant in 2024-25, with 33% having insufficient slurry storage capacity. Non-compliance can result in prosecution and unlimited fines.
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:
- Minimum distance from inland or coastal waters
- 10 metres
- Minimum design life
- 20 years (with proper maintenance)
- Below-ground silage effluent tanks
- 20 years without maintenance
- Pre-construction notification period
- 14 days advance notice to Environment Agency
The 10-metre separation applies to all silos, slurry storage systems, and fuel oil stores. Drains and sealed pipes can be within 10 metres only if the Environment Agency agrees in writing. Larger safety zones may be required near water supply intakes.
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:
- SSAFO baseline (non-NVZ)
- 4 months capacity
- NVZ minimum (cattle slurry)
- 5 months capacity
- NVZ minimum (pig and poultry slurry)
- 6 months capacity
- Storage period calculation
- 1 October to 1 April
Your storage calculation must include:
- Slurry from housed livestock
- Rainwater falling or draining into the store
- Washings from buildings and yards
- Capacity of any other slurry storage on the premises
Use the AHDB Slurry Wizard to calculate your requirements based on livestock numbers and local rainfall data. Add 25% to your calculation to allow for wetter than average winters.
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:
- Steel or concrete stores
- 300mm minimum freeboard
- Earth-banked stores (lagoons)
- 750mm minimum freeboard
- Reception pit capacity
- 2 days of slurry production (including rainfall)
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
If your land is in a Nitrate Vulnerable Zone (NVZ)
NVZs cover approximately 55% of agricultural land in England. If your land is designated, you need more storage capacity than the SSAFO baseline:
- Cattle slurry: 5 months minimum (versus 4 months SSAFO)
- Pig and poultry slurry: 6 months minimum
The longer closed periods in NVZs mean you cannot spread during winter months. You must have enough capacity to hold all slurry produced without needing to spread during prohibited periods.
Check if your land is in an NVZ using the GOV.UK interactive map.
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:
- Silo up to 1,500 cubic metres
- 20 litres per cubic metre of silo capacity
- Silo over 1,500 cubic metres
- 30 cubic metres + 6.7 litres per cubic metre over 1,500
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
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Prepare notification documentation
Gather details of the type of silo or storage system and proposed location. Include a site plan drawing and design drawing with materials specification. For prefabricated products, obtain manufacturer's specifications and guarantee.
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Submit notification at least 14 days before construction
Contact the Environment Agency general enquiries (03708 506 506 or enquiries@environment-agency.gov.uk). Submit in writing, specifying the type of storage and location. The 14-day period starts when the EA receives your notification.
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Respond to any EA requests
The EA may request additional design drawings, BS 5502 compliance confirmation, soil analysis for earth-banked stores, or installer certification for underground tanks. Provide these promptly.
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Await EA response or proceed after notification period
The EA may inspect the proposed location, request modifications, or agree the design. If you receive no response within 14 days, you may proceed with construction (but you remain subject to all regulatory requirements).
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Complete construction to required standards
Build to BS 5502 specifications, ensuring 20-year design life. Keep all construction records for future reference or inspections.
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. The penalty is a Level 2 fine (up to GBP 500). 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
The pre-1991 exemption is lost if you make substantial changes (structural alterations, increased capacity, or relocation). The Environment Agency can also serve a Regulation 7 notice requiring improvements if your structure poses a significant pollution risk.
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
- Cross-compliance or conditionality audits (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
- 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
- Check construction standards: Inspect stores for cracks, damage, or non-compliant features (missing valves, inadequate freeboard)
- Determine NVZ status: Use the GOV.UK interactive map to check if your land is in a Nitrate Vulnerable Zone
- Plan any upgrades: If storage is inadequate, investigate Slurry Infrastructure Grant funding before planning works
- Notify the EA: Submit notification at least 14 days before any construction or substantial modification
- Maintain records: Keep construction records, maintenance logs, and any EA correspondence