Statutory guidance

SR2024 No 2: generic risk assessment for using unbound incinerator bottom ash aggregate (IBAA) in construction as a deposit for recovery operation

Updated 20 May 2026

Applies to England

The risks covered in this generic risk assessment are those which are associated with the activity covered in standard rules set SR2024 No 2. The risk assessment covers the source, harm and pathway of the risk. The judgement of the risk and the risk management covered in the permit to reduce the magnitude of the risk. Any residual risk after management of the risk will be controlled by compliance.

Standard rule set SR2024 No 2 only applies to the use of IBAA (or IBAA blended with primary aggregates) produced from incinerator bottom ash (IBA) from the incineration of municipal (household and business) solid waste. The majority of IBA consists of brick, rubble, glass, ceramics and stone.

IBA is processed to remove ferrous and non-ferrous metals and graded to produce IBAA which meets the specification of the customer and associated construction activity. IBAA is used as an alternative to primary or quarried aggregates.

The construction activities in which IBAA can be used are:

• building a road sub-base
• building a structural platform
• pipe bedding

1. Risk to local human population

1.1 Release of particulate matter (dusts), which travel through the air and can be inhaled

The harmful consequences if things go wrong is the harm to human health (respiratory irritation and illness). The Environment Agency has assessed the:

• likelihood of this contact to be medium
• overall severity of potential consequence to be medium
• overall risk rating to be medium
• magnitude of this risk after management to be low

IBAA is used as a substitute for non-waste aggregates. Typical construction activities can produce dust from movement of vehicles and tipping operations especially in dry and windy weather. To manage the risk, construction activities are usually subject to method statements to ensure all operations are managed and operated with minimal impact. This should include measures to prevent and reduce risk of dust being produced and, where it is produced, from leaving the site boundaries. Where IBAA is used, the standard rules requires this approach.

1.2 Release of particulate matter (dusts) which travel through the air and then deposit on surfaces

The harmful consequences if things go wrong is nuisance (such as dust on cars and clothing). The Environment Agency has assessed the:

• likelihood of this contact to be medium
• overall severity of potential consequence to be low
• overall risk rating to be medium
• magnitude of this risk after management to be low

The activities may produce dust from movement of vehicles and tipping operations especially in dry and windy weather. Activities shall be managed and operated in accordance with a management system that includes measures to prevent and reduce risk of dust being produced and where it is produced from leaving the site boundaries. Rules can be invoked to require a particulate management plan.

1.3 Risk that hydrogen can evolve from natural chemical reactions with any aluminium

Hydrogen is lighter than air and readily disperses. The placement restrictions ensure hydrogen does not accumulate in voids or is used under buildings occupied by people or gardens.

1.4 Waste, litter and mud on local roads

Waste, litter and mud on local roads from vehicles entering and leaving the site.

The harmful consequences if things go wrong are nuisance, loss of amenity and road traffic accidents. The Environment Agency has assessed the:

• likelihood of this contact to be low
• overall severity of potential consequence to be low
• overall risk rating to be low
• magnitude of this risk after management to be low

IBAA is not associated with litter although other construction activities may. However, to manage the risk, emissions of substances not controlled by emission limits in the standard rules should be minimised in the management system.

1.5 Odour

Odour which travels through the air and can be inhaled.

The harmful consequence if things go wrong are nuisance and loss of amenity. The Environment Agency has assessed the:

• likelihood of this contact to be very low
• overall severity of potential consequence to be very low
• overall risk rating to be very low
• magnitude of this risk after management to be very low

IBAA has a low potential to produce odour. The management system should contain procedures to prevent non-permitted wastes being deposited at site and to deal with rogue loads if they do occur. There is a dormant Rule that can be utilised if odour should be a problem.

1.6 Noise and vibration

Noise and vibration which travel through air and vibration through the ground.

The harmful consequences if things go wrong are nuisance, loss of amenity and loss of sleep. The Environment Agency has assessed the:

• likelihood of this contact to be medium
• overall severity of potential consequence to be medium
• overall risk rating to be medium
• magnitude of this risk after management to be low

Noise and vibration shall be minimised and not cause nuisance. A noise and vibration management plan may be required.  

1.7 Pests

Pests (including scavenging animals, birds and other pests for example, flies) which travel through the air and over land.

The harmful consequences if things go wrong are harm to human health, nuisance and loss of amenity. The Environment Agency has assessed the:

• likelihood of this contact to be very low
• overall severity of potential consequence to be very low
• overall risk rating to be very low
• magnitude of this risk after management to be very low

IBAA will not attract pests. Risk limited by permitted waste types and good onsite management practices detailed in management system of non-conforming wastes.

1.8 Flooding of the site

Flooding of the site from flood waters.

The harmful consequences if things go wrong is the potential for waste to be washed off site and contaminated buildings, gardens, natural habitats downstream. The Environment Agency has assessed the:

• likelihood of this contact to be low
• overall severity of potential consequence to be low
• overall risk rating to be low
• magnitude of this risk after management to be low

Activities are not permitted within proximity to a watercourse or to be deposited sub-water table. The written management system should identify and minimise risks of pollution, including those arising from operations, maintenance, accidents, incidents and non-conformances.

1.9 Arson and vandalism

Arson and vandalism causing the release of polluting materials to air (smoke or fumes), water or land.

This can cause smoke to travel through the air, spillages and contaminated firewater to run-off from the site and through surface water drains and ditches. The harmful consequences if things go wrong are respiratory irritation, illness and nuisance to local population. It could lead to injury of staff, firefighters or arsonists and vandals as well as pollution of water or land. The Environment Agency has assessed the:

• likelihood of this contact to be low
• overall severity of potential consequence to be medium
• overall risk rating to be low
• magnitude of this risk after management to be low

IBAA has a very low-risk of combustion. Site machinery and fuels and oils are more of a risk but quantities would typically be low. The written management system should identify and minimise risks from unauthorised access and site security measures identified to prevent such access. The system should also describe how any polluting liquids or materials will be stored safely.

1.10 Accidental fire

Accidental fire can cause polluting materials to travel through the air (smoke or fumes) water or land.

Spillages and contaminated firewater can run-off site through surface water drains and ditches. The harmful consequences if things go wrong are respiratory irritation, illness and nuisance to local population. It could lead to injury of staff, firefighters as well as pollution of water or land. The Environment Agency has assessed the:

• likelihood of this contact to be low
• overall severity of potential consequence to be medium
• overall risk rating to be low
• magnitude of this risk after management to be low

IBAA has a very low-risk of combustion. Site machinery and fuels and oils are more of a risk but quantities would typically be low. The written management system should identify and minimise risks from unauthorised access and site security measures identified to prevent such access. The system should also describe how any polluting liquids or materials will be stored safely.

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

2.1. Heavy metals

Heavy metals may leach out of IBAA over time.

Subject to the placement restrictions set out in the standard rules, independent leachability testing has been carried out on a representative number of IBAA samples and the results modelled in a variety of groundwater scenarios. The Environment Agency is satisfied that the impact on groundwater and surface water from the use of IBAA is understood and is low.

The standard rules set back distance and other restrictions ensure IBAA is used in low sensitivity locations to leaching and subsequent movement of heavy metals in groundwater, and from run-off to surface water.  

3. Risk to groundwater

3.1 Spillage of liquids, leachate from waste, contaminated rainwater run-off transported through soil and groundwater then extraction at borehole

The harmful consequences if things go wrong is the contamination of public or private water supplies requiring treatment of water or closure of the borehole. The Environment Agency has assessed the:

• likelihood of this contact to be medium
• overall severity of potential consequence to be medium
• overall risk rating to be medium
• magnitude of this risk after management to be low

No liquid waste types are allowed under the standard rule set.

The rules do not allow deposit in groundwater source protection zones 1 or 2, or if a source protection zone has not been defined, then not within 250 metres of any well, spring or borehole used for the supply of water for human consumption. This includes private water supplies. The waste must also not be deposited in any controlled or surface waters or sub-water table. A mandatory waste acceptance procedure rule has been imposed to make sure a minimum standard is set. Mandatory operating techniques further limit the use of wastes. The management system should set out any additional stringent waste acceptance procedures to ensure only waste listed in the Rules are deposited on site. The procedures must also set out how to deal with rogue or non-conforming loads.

4. Risk to protected sites (European sites and SSSIs)

4.1. Harm to protected sites from any source

Harm to protected sites from any source such as toxic contamination, nutrient enrichment, smothering, disturbance and predation from any pathway such as air, land or water. The Environment Agency has assessed the:

• likelihood of this contact to be low
• overall severity of potential consequence to be medium
• overall risk rating to be medium
• magnitude of this risk after management to be low

The rules do not allow activities to take place within:

• 500 metres of a European Site or a Site of Special Scientific Interest (SSSI) unless designated for geological or physicographical purposes
• 250 metres within the presence of Great Crested Newts where it is linked to the breeding ponds of the newts by good habitat
• 50 metres of a site that has species or habitats protected under the Biodiversity Action Plan that the Environment Agency considers at risk to this activity
• 50 metres of a National Nature Reserve, Local Nature Reserves, Local Wildlife Site, Ancient woodland or Scheduled Ancient Monument

Explanation of terms

Receptors

Receptors to consider should include atmosphere, land, surface waters, groundwater, humans, wildlife and their habitats. A single receptor may be a risk from several different sources and all must be addressed.

Source

The source of the hazard will be the activity or operation taking place for which a particular hazard may arise.

Harm

Harm may arise when a specific hazard is realised.

Pathways

Pathways are the routes or means by which defined hazards may potentially realise their consequences at the receptors.

Likelihood of exposure

The probability of exposure is the likelihood of the receptors being exposed to the hazard. Example definitions:

• high – exposure is probable: direct exposure likely with no or few barriers between hazard source and receptor
• medium – exposure is fairly probably: feasible exposure possible – barriers to exposure less controllable
• low – exposure is unlikely: several barriers exist between hazards source and receptors to mitigate against exposure
• very low – exposure is very unlikely: effective, multiple barriers in place to mitigate against exposure

Consequences

The consequences of a hazard being realised may be actual or potential harm. This will include being on a high, medium, low or very low score using attributes and scaling to consider ‘harm’.

Magnitude

The magnitude of the risk is determined by combining the probability with the magnitude of the potential consequences:

• high risks require additional assessment and active management
• medium risks require additional assessment and may require active management and monitoring
• low and very low risk require periodic review

Risk management

Risk management involves breaking or limiting the source-pathway – receptor linkage to reduce risk.