Statutory guidance

SR2021 No 4: generic risk assessment for composting in closed systems – installations

Updated 17 July 2023

Applies to England

SR2021 No 4 generic risk assessment for a Part A installation: composting in closed systems with a treatment capacity of:

• less than 75,000 tonnes each year
• more than 75 tonnes each day

The Environment Agency produces the generic risk assessments for all standard rules permits. These list the potential risks and specify the measures (but not limited to) to manage them.

Check this generic risk assessment to understand:

• the potential risks of in vessel composting (with or without elements of open storage and processing)

• if your proposed activity has the same risks and can you apply for the standard rules permit

• how to manage the risks effectively

Each risk comprises:

• information about the source, pathway and receptor – and the potential harm to that receptor

• a judgement of the level of risk and justification of that judgement

• actions for managing the risk (through permitting) and a residual risk rating after managing it

Risk management involves breaking or limiting the source-pathway-receptor linkage to reduce the risk. If we set minimum distances we explain the basis of the distance, for example by modelling.

We will control the residual risk (after risk management) when we assess compliance.

If you need to check the meaning of any terms we have used (in the context of this risk assessment), see the explanation of terms.

This generic risk assessment is based on the following parameters.

Parameter 1

These permitted activities:

• acceptance and storage of waste prior to composting (R13)
• composting including screening and shredding (R3)
• recycling and reclaiming organic substances which are not used as solvents (R12) – excludes temporary storage, pending collection. on the site where it is produced

Parameter 2

These permitted waste types:

• non-hazardous including biodegradable wood, vegetable matter and animal manure, cooked food waste and animal wastes covered by the Animal By-Products Regulations and only those wastes listed in the permit

Parameter 3

Quantity of waste accepted at the facility is less than 75,000 tonnes each year, including not more than 10 tonnes of animal waste each day and limited to the design capacity of the site.

Parameter 4

All non-compostable plastics will be removed to as low as is reasonably practicable before processing.

Parameter 5

All incoming waste shall be stored and treated on an impermeable surface in an enclosed building with sealed drainage system with an appropriately designed and maintained abatement system (as required by the permit).

Parameter 6

Secondary containment is risk assessed and follows the recommendations of the CIRIA 736 report.

Parameter 7

The only point source discharges to controlled waters are clean surface water from the roofs of buildings and from areas of the facility not used for the storage or treatment of wastes. There are no other direct or indirect discharges permitted.

Parameters 8 to 15

The activities shall not be carried out within:

• 250 metres of the nearest sensitive receptor
• 500 metres of a European site (within the meaning of Regulation 8 of the Conservation of Habitats and Species Regulations 2017) or a Site of Special Scientific Interest, including candidate or proposed sites or Marine Conservation Zone
• 250 metres of the presence of great crested newts, where it is linked to the breeding ponds of the newts by good habitat.
• within 10m of a water course
• within a groundwater source protection zone 1 and 2, or if a source protection zone has not been defined then within 250 metres of any well, spring or borehole used for the supply of water for human consumption. This must include private water supplies.
• 50 metres of a Local Nature Reserve, Local Wildlife Site, Ancient Woodland or Scheduled Monument
• 50 metres of a site that has species or habitats of principle importance (as listed in Section 41 of the Natural Environment and Rural Communities Act 2006) that the Environment Agency considers at risk to this activity.
• an Air Quality Management Area

Parameter 16

The only point source emissions into surface or groundwater are surface water from roofs of buildings and areas of the facility not used for storing or treating wastes.

Parameter 17

All enclosed treatment areas shall have a designed and managed air abatement system.

1. Risk to local human population

1.1 Release of particulate matter (dust) and micro-organisms (bioaerosols)

Dust and bioaerosols travel through the air and can be:

• inhaled, ingested or inoculated
• deposited on garden fruit and vegetables and then ingested

There is a risk of dust and bioaerosols causing:

• respiratory irritation and illness
• gastro-intestinal illness

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because:

• composting activities produce and release bioaersosols, such as micro-organisms
• there is potential for exposure to anyone living or working close to the site (excluding operator and employees) from any activities taking place in the open and from bio-filters and emission point sources

Managing the risk

Composting produces dust, powders and loose fibres, therefore activities shall not be carried out:

• within 250 metres of the nearest sensitive receptor

• in an Air Quality Management Area

Sanitisation of waste takes place in a building or in vessels.

Most dust will be washed off by rain or during food preparation.

The permit requires emissions of substances not controlled by emission limits (excluding odour) shall not cause pollution.

The following actions also need taking:

• all appropriate measures shall be followed as documented in the management system, and if required an emissions management plan submitted and a risk assessment review done

• the emissions management plan and risk assessment review are implemented as needed

• all relevant Best Available Techniques (BAT) conclusions and BAT Associated Emissions Limits (AELs) (as set out in the BAT Reference Document (BREF)) shall be complied with and relevant appropriate measures shall be employed

• the bio-filter or an equivalent abatement system shall be specifically designed, monitored and maintained to minimise the release of bioaerosols, micro-organisms and particulates

• weather conditions are monitored continuously and activities do not take place when the wind direction is towards the sensitive receptor

• materials treated and stored in the open shall be monitored to prevent high temperatures and dry conditions developing

• controlling the temperature and moisture of the material on site

Permitted waste types do not include dusts, powders or loose fibres. However composting activities can cause dust therefore continuous dust monitoring shall be deployed if required, including:

• outdoor windrows and piles shall be positioned to prevent wind stripping

• surfaces shall be kept free of debris and damped down using clean water during dry weather

• housekeeping shall take place to prevent build-up of dry dusty materials and rotting waste

• screened material shall be covered as necessary

Taking these actions will control the risk and rate it as ‘low’.

1.2 Waste, litter and mud on local roads

Vehicles entering and leaving the site risk causing:

• nuisance
• loss of amenity
• road traffic accidents

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because:

• there is a risk of creating unsafe road surfaces in wet weather
• local residents are often sensitive to mud on roads

Managing the risk

Risk management is the same as risk 1.1 along with:

• all incoming and outgoing waste or material will be sheeted

• appropriate measures could include clearing waste, litter and mud arising from the activities from affected areas outside the site

• roads to be swept and damped down as necessary

• wheel wash facilities are made available due to the ABPR waste allowed

Taking these actions will control the risk and rate it as ‘low’.

1.3 Odour

Odour travels through the air and can be inhaled. There is a risk of causing:

• nuisance
• loss of amenity

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as high
• overall severity of potential consequences as high
• overall risk rating as high

The reasons for giving the activity this rating is because:

• composting produces and is likely to release unpleasant odour and emissions if allowed to become anaerobic
• of the potential for exposure to anyone living or working close to the site (excluding operator and employees)
• local residents are sensitive to odour

Managing the risk

To manage the risk the standard rules permit requires:

• waste acceptance only where there is capacity to treat the wastes – the maximum waste limits are set by these rules
• storage, physical treatment and composting of wastes under anaerobic conditions shall be prevented by adopting BAT and other appropriate measures – includes meeting AELs
• an odour management plan including use of appropriate measures to reduce odour problems such as minimising storage times before processing and contingency arrangements for smelly wastes delivered from site to a permitted facility
• process controls shall be in line with a fully implemented management system which ensures operational conditions are optimised and maintained from waste acceptance and throughout the whole process, including an odour management plan review as necessary
• sanitisation of wastes shall take place in a closed system incorporating a bio-filter or an equivalent abatement system (designed by a qualified engineer for the capacity and volume of waste – to minimise the release of odour and ensuring it is fit for purpose)
• abatement systems shall be monitored an managed to prevent odorous conditions developing
• all waste stabilised outside shall be monitored and managed to prevent odorous conditions developing
• leachate storage lagoons and tanks are covered

Taking these actions will control the risk and rate it as ‘medium’.

1.4 Noise and vibration

Noise travels through the air and vibration through the ground. There is a risk of causing:

• nuisance
• loss of amenity for local residents and workplaces
• loss of sleep

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because local residents often sensitive to noise and vibration.

Managing the risk

To manage the risk the standard rules permit requires:

• emissions shall be free from noise and vibration at levels likely to cause pollution
• a noise and vibration management plan, revised as required

Taking these actions will control the risk and rate it as ‘low’.

1.5 Scavenging animals and birds

Animals and birds travel over land and through the air. There is a risk of causing:

• nuisance
• loss of amenity
• harm to human health from waste carried off-site and from faeces

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reason for giving the activity this rating is because the permitted food wastes may attract scavenging animals and birds.

Managing the risk

To manage the risk:

• waste can only be accepted when there is capacity to treat it

• waste shall be inspected on arrival for signs of infestation and rejected where necessary, pest infested waste is not permitted

• waste shall only be tipped in an enclosed building and prepared and treated quickly, no waste shall be stored for longer than 2 days

• use of an approved knock-down is allowed following associated guidelines

• permitted waste types include catering wastes and other wastes containing animal by-products are restricted by separate controls under the ABPR and by the standard rules permit which requires each composting batch to undergo sanitisation in a closed system

• pest control procedures shall be clearly documented in the management system

• an emissions management plan and risk assessment review may be required

• all appropriate measures shall be adopted and associated guidance followed

Taking these actions will control the risk and rate it as ‘low’.

1.6 Pests

Pests, such as flies can travel through the air or over land. There is a risk of causing:

• nuisance
• loss of amenity
• harm to human health

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because the permitted waste types attract pests, such as flies. They can multiply, particularly in the summer months when the waste is more odorous and attracts flies.

Managing the risk

To manage the risk the requirements are the same as risk 1.5 along with:

• avoidance of anaerobic conditions
• infested material is rejected and removed
• use of authorised insecticides of knock-down sprays only
• implementing and maintaining a cleaning plan – storage areas cleaned and gullies cleared of debris at least weekly

Taking these actions will control the risk and rate it as ‘low’.

1.7 Contaminated water used for recreational purposes

The human population is at risk of direct contact with or ingestion of contaminated waters.

There is a risk of contaminated water used for recreational purposes causing skin damage or gastro-intestinal illness.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

We think this risk is unlikely to occur but might restrict recreational use.

Managing the risk

To manage the risk the operator shall:

• comply with the sensitive location restrictions in the permit
• keep to the permit requirement of ‘no direct or indirect discharges are permitted from the site’ and therefore no AELs are applied
• comply with the rules on emissions of substances not controlled by emission limits
• reach sanitisation temperatures to allow pasteurization of material
• maintain adequate storage of leachates and liquors

Managing the risk in this way will control the risk and rate it as ‘low’.

2. Risk to local human population and local environment

2.1 Flooding of the site

Flood waters can flood the site.

There is a risk of waste washed off-site contaminating buildings, gardens and natural habitats downstream.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

The reasons for giving the activity this rating is because:

• the permitted waste types are non-hazardous and therefore the risk of contamination is not high
• leachate may have a high biological oxygen demand (BOD), ammonia and suspended solids

Managing the risk

Standard rules permits are not usually issued in flood risk areas.

To manage the risk the standard rules permit requires:

• compliance with the sensitive location exclusions

• a written management system that identifies and documents the process controls to minimise the risk of pollution – includes those arising from operations, maintenance, accidents, incidents and non-conformances.

Flood risk management covers:

• activation of flood risk contingency plan for diversion of waste, if required
• lagoons must have freeboard
• monitoring of local weather conditions and forecast required
• drainage plans being available on site
• emergency procedures being clearly communicated to all site operatives
• storage and treatment of wastes to take place on an impermeable surface with sealed drainage

Taking these actions will control the risk and rate it as ‘low’.

2.2 Fire risk

There is a risk of fire on-site:

• from arson and, or vandalism
• by spontaneous combustion from uncontrolled decomposition

Fire can cause:

• polluting materials (smoke or fumes) to travel through the air, water or over land
• spillages and contaminated firewater by direct run-off from the site and through surface water drains and ditches

We have assessed the potential harm as:

• respiratory irritation, illness and nuisance to the local population
• injury to staff, firefighters or arsonists and vandals
• air, water or land pollution

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because:

• rapidly decomposing material gives rise to self-heating
• material can become dry and increase combustibility

Managing the risk

To manage the risk the standard rules permit requires:

• a written management system that identifies and minimises risks of pollution, including those arising from operations, maintenance, accidents, incidents, non-conformances – therefore includes measures to avoid fire outbreak and to control fires, including containment of fire waste
• a fire prevention plan must be submitted if required
• that permitted waste types are organic and non-hazardous
• a robust waste acceptance procedure
• no burning of wastes
• compliance with the limits to the feedstock waste material and composting to the design capacity of the site
• monitoring and controls of composting moisture and temperature (preventing excessive temperatures), and the need to act swiftly if temperatures increase (includes stored finished material and oversize material)
• monitoring is undertaken to demonstrate a representative core temperature
• finished compost to be monitored and stable
• oversize material to be monitored
• adequate fire breaks around material
• site security
• water supplies to be available for fire fighting, including storage of fire-fighting water
• site drainage, including clean water drainage to be identified and documented within the management system

Taking these actions will control the risk and rate it as ‘low’.

3. Risk to local human population, livestock and wildlife

3.1 Litter on surrounding land and in final material

Litter can travel through the air and then be deposited on land. There is a risk of causing:

• nuisance
• loss of amenity
• harm to animal health
• reduction in land bank values due to contamination

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reasons for giving the activity this rating is because:

• local residents are sensitive to litter
• plastic contamination in compost reduces land values and economic market certainty
• plastic contamination can harm grazing animals and soil quality

Managing the risk

To manage the risk the standard rules permit requires:

• keeping to the waste types in the permit and the controls on contamination of non-compostable plastic and litter
• a management system with waste pre-acceptance and acceptance procedures that reduce the risk of accepting waste heavily contaminated with waste plastic
• compliance with the ‘emissions of substances not controlled by emission limits’ rule, submitting an emissions management plan, if necessary
• waste rejection of heavily contaminated feedstock
• removing non-compostable plastic and litter to as low as reasonably practicable as waste arrives and before processing
• picking litter in windrows and affected areas
• safe storage of waste to prevent cross-contamination from non-conforming waste
• covering waste skips, including those containing non-conforming waste
• assessing the effectiveness of plastic removal and the quality of the finished material

Taking this action will control the risk and rate it as ‘low’.

3.2 Gaining unauthorised access to site

There is a risk of direct physical contact with all on-site hazards such as wastes, machinery and vehicles.

There is a risk of causing injury to humans or livestock.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

The reasons for giving the activity this rating is because the:

• permitted wastes are non-hazardous
• standard rules permit does not allow unpermitted entry to the site
• management system includes procedures for worker and visitor safety

Managing the risk

To manage the risk the standard rules permit requires:

• activities shall be managed and operated in accordance with all appropriate measures and a documented and implemented management system that stipulates all preventative measures and emergency responses should accidents occur (including site security measures to prevent unauthorised access)

• roles and responsibilities are clearly laid out and staff training is provided (will include site security measures to prevent unauthorised access)

• emergency contact details shall be displayed at the site entrance

• pedestrian walkways shall be clearly marked

• visitors should receive a health and safety induction when visiting and must follow the site operator’s instructions

Taking this action will control the risk and rate it as ‘very low’.

4. Risk to surface waters close to and downstream of site

4.1 Risk of pollution causing acute effects

There is a risk of pollution from spillage of liquids, leachate from waste, contaminated rainwater run-off from waste with high organic and ammonia content and suspended solids.

Contamination can travel through direct run-off from site over the land, surface water drains and ditches.

We have assessed the acute effects as follows:

• oxygen depletion
• fish kill
• algal blooms

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as medium
• overall severity of potential consequences as medium
• overall risk rating as medium

The reason for giving the activity this rating is because:

• there is potential for contaminated rainwater run-off from waste operations, especially during heavy rain
• leachate may have a high BOD, ammonia and suspended solids
• the permitted waste types are non-hazardous, sludges or liquids

Managing the risk

To manage the risk the standard rules permit requires:

• all operations shall be more than 10 metres from a watercourse and excluded from SPZ 1 and 2

• a written management system that identifies and documents the process controls to minimise the risk of pollution – includes those arising from operations, maintenance, accidents, incidents and non-conformances

• storage and treatment of wastes to take place on an impermeable surface with sealed drainage

• all liquids must be in containers with secondary containment

• all secondary containment where required, based on a site-specific risk assessment meeting CIRIA 736

• run-off is restricted by the ‘emissions of substances not controlled by emissions limits’ condition, (excludes odour)

• appropriate measures to be followed, such as controls to prevent over-filling of storage systems to maintain lagoon freeboard

• flood risk contingency plan for diversion of waste can be activated

• drainage plans will be available on site

• local weather conditions and forecast must be monitored

• emergency procedures will be clearly communicated to all site operatives

Taking these actions will control the risk and rate it as ‘low’.

4.2 Risk of pollution causing chronic effects

There is a risk of pollution from:

• liquid spills
• leachate from waste
• contaminated rainwater run-off from waste with a high organic and ammonia content and suspended solids content
• loss of containment from on-site storage

Contamination can travel by:

• direct run-off from site over the land, through surface water drains and ditches
• indirect run-off through soil

We have assessed the chronic effect as deterioration to water quality.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

The reason for giving the activity this rating is because pollution is likely to be detected quickly.

Managing the risk

To manage the risk, take the actions for risk 4.1 along with:

• all liquids must be in containers with secondary containment

• run-off is restricted by the ‘emissions of substances not controlled by emission limits’ condition (excludes odour)

• using drainage plans to separate clean and dirty water

• considering this risk in an accident management plan

Taking these actions will control the risk and rate it as ‘very low’.

5. Risk to water abstracted from a watercourse

These risks relate to watercourses downstream of a facility and to water for agricultural or potable use.

This receptor is at risk from:

• liquid spills

• leachate from waste

• contaminated rainwater run-off from waste with high organic content

There is a risk of contaminants travelling through direct run-off from the site across ground surface, via surface water drains and ditches and finally through abstraction. This could have acute effects and cause the closure of abstraction intakes.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

The reason for giving this rating is due to the potential for contaminated rainwater run-off from outside waste operations, especially during heavy rain.

Managing the risk

To manage this risk, take the actions set out in risks 4.1 and 4.2.

Taking these actions will control the risk and rate it as ‘very low’.

6. Risk to groundwater

Groundwater is at risk from:

• liquid spills
• leachate from waste
• contaminated rainwater run-off from waste with high organic and ammonia content

There is a risk of contaminants travelling through soil and groundwater which can then be abstracted from a borehole. This could have a chronic effect resulting in the groundwater requiring treatment or causing closure of a borehole.

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

We have given this rating because of the potential for contaminated rainwater run-off or leachate from waste operations, especially during heavy rain. The consequence is based on the possibility of pollution not being detected for a long time.

Managing the risk

To manage the risk the following actions must be taken:

• the activities shall not be carried out within a groundwater SPZ 1 and 2, or if a SPZ has not been defined then within 250 metres of any well, spring or borehole used for the supply of water for human consumption (including private water supplies)

• maintaining freeboard

• where secondary containment is required it’s based on a site specific risk assessment and meets CIRIA 736 standards

• any storage lagoons must meet CIRIA 736 or an equivalent standard

• periodic monitoring as required by the permit

Taking these actions will control the risk and rate it as ‘very low’.

7. Risk to protected sites

Protected sites include:

• National Parks and Areas of Outstanding Natural Beauty
• Marine Conservation Zones
• Sites of Special Scientific Interest
• Special Areas of Conservation
• Special Protection Areas
• Ramsar wetland sites

Protected sites can be at risk from any source and by any pathway.

The risk of harm to protected sites include (but are not limited to) the following:

• nutrient enrichment
• leachate
• contaminated surface water run off
• smothering
• disturbance
• predation

Judgement of risk

We have judged the:

• likelihood of the hazard affecting the receptor as low
• overall severity of potential consequences as low
• overall risk rating as low

The reasons for giving the activity this rating is because waste composting operations may cause harm to and deterioration of nature conservation sites.

Managing the risk

To manage the risk we require compliance with the standard rules permit, including:

• applying exclusion distances

Taking this action will control the risk and rate it as ‘low’.

Explanation of terms

Receptor

The things at risk and that need protecting.

Receptors considered include atmosphere, land, surface waters, groundwater, humans, wildlife and their habitats.

A single receptor may be at risk from several different sources and all must be addressed.

Source

The agent or process that has the potential to cause harm.

A contaminant or pollutant (a hazard) that has the potential to cause harm. For example, the activity or operation taking place for which a particular hazard may arise.

Harm

The harmful consequence to the receptor if the hazard is realised.

Pathways

The route or means by which a defined hazard may affect a receptor.

Source-pathway-receptor linkage

There has to be a link between the source, pathway and receptor for there to be a risk.

Likelihood of exposure

This is the likelihood of the receptors being exposed to the hazard. The meaning of the definitions are:

• high – exposure is probable – direct exposure is likely with no or few barriers between the hazard source and the receptor

• medium – exposure is fairly probable - feasible exposure is possible as the barriers to exposure are less controllable

• low – exposure is unlikely – several barriers exist between the hazard source and receptor to reduce exposure

• very low – exposure is very unlikely – effective, multiple barriers are in place to reduce exposure

Overall magnitude of potential consequence

This is the severity of the consequence if the hazard is realised and may cause actual or potential harm.

This will have a high, medium, low or very low rating using attributes and scaling to consider ‘harm’.

Risk rating

We work out the risk rating by combining the likelihood of exposure with the magnitude of the potential consequences.

We assign these ratings:

• high risk – requires additional assessment and active management

• medium risk – requires additional assessment and may need active management and, or monitoring (or both)

• low and very low risks will require a periodic review