Silage and slurry storage
You must follow these rules if you store silage or slurry. You may also be required to meet these rules for other organic materials such as digestate.
You need to know the general rules that apply if you store any of the organic manures or silage as defined in the Water Resources (Control of Agricultural Pollution)(Wales) Regulations 2021, as well as the specific rules for storing and handling each one.
Transition periods currently apply to certain measures within the Regulations. The Welsh Government provide further details.
Farms within previously designated nitrate vulnerable zones
If your farm was within a nitrate vulnerable zone (NVZ), designated prior to 1 April 2021, you must comply with the requirements immediately - the transition periods within the regulations do not apply.
The Water Resources (Control of Agricultural Pollution)(Wales) Regulations 2021 replaced the NVZ requirements.
Let us know
You must let us know of any substantial changes to your storage facility at least 14 days before construction begins.
You are responsible for making sure you meet the rules. The rules apply to you if you control, manage or look after a farm or an installation on a property, for example as a:
- farmer or land manager
- tenant farmer – unless you can prove someone else, for example the landowner, is jointly or wholly responsible
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 system that is underground must be designed and constructed to last at least 20 years without maintenance)
- not be within 10 metres of any inland and coastal waters eg, streams, ditches, ponds or any pipes or culverts
- not be within 50 metres of any borehole, well or spring
- not be within a groundwater source protection zone 1 (SPZ1) unless site-specific mitigation measures that minimise the risk to drinking water supplies have been agreed in writing with Natural Resources Wales
In sensitive locations, where there is a risk of causing pollution of groundwater and surface water, the above minimum distances will need to be increased.
Substantial change includes increasing the size of storage facility or any work that results in structural alterations, but does not include minor repairs.
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 is exempt from the rules for new stores. However, if you make substantial changes, for example structural changes, increasing capacity or relocating , then your store is no longer exempt from complying with the rules.
Natural Resources Wales can also serve a notice at any time requiring you to bring storage up to the current standards if it believes there is a significant risk of pollution to controlled waters.
Before you start work
Find out what permissions you need. This is your responsibility. You need to be clear on what work is needed and what permissions are required from which authorities.
Before you make a planning application or submit your pre-construction notification, you can ask us for preliminary advice.
In locations that are sensitive to air emissions of ammonia from the storage of silage or slurry, additional information will be required.
Produce a design plan and provide it to us at least 14 days before you begin construction of a new store for slurry or silage including field silage sites, or make substantial changes to an existing store.
Producing a design plan and notifying us
The best way to demonstrate compliance with the requirements of the regulations is to use suitably qualified people (for example a Chartered Engineer) to design, oversee and validate construction of all aspects of the storage infrastructure.
A design plan must include:
- qualifications of the persons who have produced the design and who will oversee and validate the construction
- drawings of your proposed storage showing the location, dimensions and cross-sections of the structure.
- a detailed design description with reference to any stability assessments.
- specification of the proposed materials you will use to construct the store, including copies of the manufacturer’s specification, guarantee, and any certification and compliance testing required by the guidance.
- 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 tanks you’ll need certification from the installer – you must provide this to Natural Resources Wales because the tank needs to perform for at least 20 years without maintenance
- how you will verify that the structure has been built as per the design plan
Silage Specific Rules
There are specific rules you must follow 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 any inland or coastal waters eg streams, ditches, ponds or any pipes or culverts.
In addition, you must not store field silage within 50 metres of a protected water supply source or within a groundwater source protection zone 1 (SPZ1). These are places where water is abstracted (taken) for any of the following purposes:
- human consumption
- use in farm dairies
- human food preparation.
Your silo must have:
- an impermeable base extending beyond any walls
- impermeable drainage collection channels around the outside, flowing into an effluent tank.
- all parts of a silo must be resistant to attack by the silage effluent
The base must comply with:
- BS EN 1992-1-1:2004+A1:2014 Eurocode 2 Design of concrete structures (for concrete bases)
- BS EN 1992-3:2006 Eurocode 2. Design of concrete structures. Liquid retaining and containing structures
- BS EN 13108-4:2016 Bituminous mixtures. Material specifications. Hot rolled asphalt (for hot-rolled asphalt bases)
If your silo has walls, they must withstand wall loadings set in British Standard 5502-22:2003+A1:2013.
To ensure your design and construction meets these required standards you should request written confirmation from the installer, manufacturer, or check the manual that came with your equipment,
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 must 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 silage effluent with 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.
The minimum capacity rules for effluent tanks should give you at least two days storage at peak flow. However, it’s up to you to ensure you’ve enough capacity to avoid the risk of pollution. If rainwater also collects in the silage effluent tank, this must be accounted for in the capacity
|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
Baled silage must be sealed in an impermeable membrane or bagged. It does not need a specially constructed base, but you must make sure any silage stored directly on the ground doesn’t result in effluent causing pollution of surface or groundwater.Baled silage
Baled silage must not be stored within 10 metres of any surface 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, and topsoil must not be disturbed.
If you make field silage or non-baled bags, you must:
- choose a suitable site taking into account but not limited to: slope, soil permeability, risk of causing pollution to surface, groundwater or protected sites eg Sites of Special Scientific Interest (SSSI)
- the place is at least 10 metres from any inland or coastal waters eg streams, ditches, ponds or any pipes or culverts
- at least 50 metres from the nearest water abstraction point of any protected water supply source that silage effluent could enter if it escaped
- not be within a groundwater Source Protection Zone 1 unless site specific mitigation has been agreed with Natural Resources Wales
- notify Natural Resources Wales at least 14 days before you first use the site link to amended form
Slurry Specific Rules
Slurry is defined as a liquid or semi-liquid matter composed of:
- excreta produced by livestock (other than poultry) while in a yard or building (including that held in wood chip corrals); or
- a mixture wholly or mainly consisting of livestock excreta, livestock bedding, rainwater and washings from a building or yard used by livestock of a consistency that allows it to be pumped or discharged by gravity at any stage in the handling process;
There are specific rules you must adhere to for the storage of slurry, particularly for earth-banked stores.
Run-off from weeping wall stores, solid manure stores, woodchip, or straw-bedded corrals or stand-off pads are all defined as slurry.
You must collect all slurry in an appropriately constructed store or stores.
The rules do not apply to slurry you store temporarily in a container or trailer for transportation.
Where to store slurry
You must not site any part of your slurry storage system (tanks, effluent tanks, channels or reception pits) within:
- 10 metres of inland or coastal waters
- 50m of any borehole, well or spring
- A groundwater Source Protection Zone 1 (SPZ1)
unless site-specific mitigation measures that minimise the risks to water has been agreed in writing with Natural Resources Wales
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.
In some circumstances NRW may also require:
- the inclusion of floating or full covers to stores to limit ammonia release. This requirement may affect your choice or limit the size of storage
- secondary containment measures for high risk locations.
When calculating 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. Freeboard is the vertical distance between the crest of your tank or the lowest point on your lagoon bank and the slurry surface.
You will need capacity to allow for storage of all slurry produced and contaminated rainfall for The Water Resources (Control of Agricultural Pollution)(Wales) Regulations 2021 defined storage periods. Five months for cattle and six months for pigs and poultry.
What this means for you will depend on;
- when and where you use your slurry,
- how much capacity is available at the beginning of the storage period ie how you use your slurry prior to the storage period,
- the size of your tanks and expected rainfall over the storage period.
Average rainfall data (1 October to March) is available via the Welsh Government DataMapWales mapping portal based upon the met office’s 1981 – 2010 averaging period accessible. Average rainfall figures (1st October to March 31st) | DataMapWales (gov.wales) The data is provided on to a 1km grid to reflect the wide geography of Wales and provide localised data.
If you’re in an area with above average rainfall, you’ll need more capacity. Speak to Natural Resources Wales or a consultant if you’re unsure how much you’ll need.
If you operate with less than the required capacity, Natural Resources Wales may refuse to accept your proposal
Any temporary or interim storage facilities you have – such as a reception pit – must be large enough to store a minimum of two days combined slurry production and likely rainfall.
Drainage pipes from slurry store
If your slurry tank, effluent tank or reception pit is fitted with a drainage pipe, it must have two valves separated by a least one metre. Each valve must be able to shut off the flow of slurry and be locked when not in use.
The exception to this rule is 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 to form an effective barrier to leakage. You may need laboratory analysis and confirmation from a civil engineer to be sure your soil is suitable. Alternatively you can import suitable impermeable soil or use a synthetic liner.
To be suitable in situ soils (and compacted soils that form a bund or form the lining layer) must have a permeability of 1 x 10-9 metres per second (0.000001 mm per second). Testing should be to BS EN ISO 17892-11:2019or to BS EN 1997-2:2007.
CIRIA guidance C759F ‘Livestock manure and silage storage infrastructure for agriculture’ provides further guidance on how to assess the suitability of a location for an earth-banked lagoon. CIRIA C759F
The base of a weeping-wall store must extend beyond its walls and include perimeter drains of sufficient width to contain all slurry draining from the store which must be directed into a slurry system designed and constructed to meet the requirements of the regulations.
After constructing your silage or slurry storage
Before using your store, you must provide a written report to NRW to demonstrate that it has been built as per the design plan you submitted with your pre construction notification (link to form) and complies with the legal requirements. This validation report provides the final ‘as-built’ construction and engineering details of the storage infrastructure. It must be signed by a competent person who is suitably qualified (for example a Chartered Engineer)
This written confirmation must include:
- evidence that the design plan has been followed
- justifications for any changes or deviations from the original design plan
- photographs of the completed structure including during construction for earth banked lagoons
- copies of any site engineer’s daily records
- records of all test results that were completed showing compliance with the required standards.
- any other relevant site-specific information to prove the integrity of the construction
Possible action after a breach of the regulations
If a breach of the regulations is confirmed, action will be taken according to the Natural Resources Wales Enforcement and Prosecution policy and procedures. Possible action depends on the seriousness of the breach and impact on the environment. They include:
- advice on remedying a minor breach
- warning letter noting the breach, which may be taken into account in the event of a future breach
- legal notice
- formal caution
If prosecuted and convicted in either the Magistrates or the Crown Court, you may face an unlimited fine.
If you claim Basic Payment Scheme or any Rural Development Programme payments you must also observe the Common Agricultural Policy (CAP) Cross Compliance standards including the Good Agricultural and Environmental Conditions (GAEC) which aim to protect surface and ground water from pollution.
Compliance with the Water Resources (Control of Agricultural Pollution)(Wales) Regulations 2021 will form part of the cross-compliance inspection regime.
You will have to comply with the Regulations to be entitled to full payment. Failure to comply could lead to deductions.
If you’re served notice
We can serve a notice on you requiring you to take action to improve existing installations where NRW considers that there is a significant risk of pollution to ‘controlled waters’. (This can include field silage sites and otherwise “exempt” installations).
The actions required by the Notice must be appropriate to the task of reducing to a minimum any significant risk of pollution of surface or groundwater (For example, to require sufficient slurry storage to be provided.).
You will have a minimum of 28 days to comply with the Notice
We may extend this minimum period to take into account, for example, of the time needed to obtain planning permission, or to arrange for contractors to do the work, weather or site conditions
How to appeal
You may appeal to Welsh Ministers against a Notice served by NRW.
If you wish to appeal against a Notice served by us, it must be done in writing within 28 days from the day after the date on which the Notice was served.
You and NRW have the right to request an oral hearing by the person appointed to decide your appeal.
Appeals in Wales should be addressed to:
Agriculture, Sustainable Development Division Welsh Government
and copied to the us at the address given with the Notice.
Decisions on appeals
If an appeal is successful the Notice may be withdrawn or modified or the period for compliance be extended. If, following the appeal, the Notice is not withdrawn and the period for compliance is not extended, the period for compliance is deemed to expire on the day of the determination of the appeal, unless the Welsh Ministers decide to extend the period for compliance. The Welsh Ministers could bear in mind, when deciding whether to extend the period for compliance, whether it will be reasonable, feasible, or practicable for the appellant to comply with the determination as soon as it has been issued.