Guidance

Municipal incinerator bottom ash aggregate (IBAA): interim sampling and testing protocol

How you can sample and test IBAA as an alternative to a full assessment using the WM3 waste classification technical guidance.

• From: Environment Agency
• Published: 7 May 2026

Applies to England

When to use this protocol

If you process incinerator bottom ash (IBA), you must assess any incinerator bottom ash aggregate (IBAA) you produce and assign the correct hazardous or non-hazardous waste code.

You can do this by following this interim protocol, or by following the WM3 waste classification technical guidance.

This protocol gives a national framework as an alternative to full WM3 assessment. Its purpose is to:

• help you meet legal requirements
• create a consistent sector-wide approach to sampling and testing

This protocol:

• applies only to IBAA derived from IBA produced through incineration of municipal waste
• requires the input IBA to be non-hazardous
• runs for an initial 12 months from 1 April 2026, and then continues until the Environment Agency withdraws or changes it

If you cannot comply with this protocol, you must follow the requirements in the WM3 waste classification technical guidance.

Notify the Environment Agency

If you want to use and comply with the interim protocol, you must email the Environment Agency at wcrespond@environment-agency.gov.uk with:

• a list of sites that will use the protocol, including permit number and address
• a contact name, email address and telephone number for each site
• results of any start-up sampling data you have already obtained
• speciation figures that will be applied to each of your facilities
• your chosen sampling programme (12 or 24 samples)

You must provide every sampling and testing result to the Environment Agency at wcrespond@environment-agency.gov.uk within 2 working days of receipt. Include ‘IBAA interim protocol – sampling result’ in the subject line.

Planning your sampling schedule

You can use one of the following sampling cycle options:

• option 1: 12 rolling sample set
• option 2: 24 rolling sample set

You must tell the Environment Agency what your chosen sampling cycle is before you begin using the protocol.

You must take samples monthly and spread them throughout the year.

If you do not take a sample in any given month, you must record this as an exceedance. If you follow the 24 rolling sample set, you must record this as 2 exceedances.

You must provide sampling results for each IBAA output you produce. If you produce 2 different outputs (for example 0 to 16mm and 0 to 60mm), you must maintain 2 separate rolling sets of samples.

Using historical data

You can use sampling results from 2019 onwards as start-up data if the samples were taken and tested in line with the Environmental Services Association (ESA) sampling and testing protocol for municipal IBA. If historical data is available, you must use the most recent results.

If one of your sites has no suitable historical data, or has an insufficient number of samples, you must carry out accelerated sampling and testing to generate a start-up dataset. The amount of start-up samples you need depends on your chosen sampling cycle.

Option 1: 12 rolling sample set

Option 1 requires 12 start up samples per IBAA output. If you already have this data before the start of the protocol then you only need to take 1 random sample per IBAA output each month from 1 April 2026.

If you do not have historical sample data to use as start-up sampling:

• take 2 samples per month for the first 6 months to generate 12 start‑up data points
• then take 1 sample per month for the remaining 6 months (18 total samples in year 1)
• continue with 1 sample per month thereafter

If you have some existing data from 2019:

• take 2 samples per month until you reach 12 data points
• then take 1 sample per month for the remainder of the year and until the protocol is reviewed (for example, if you already have 10 samples, take 2 samples in the first month)

Option 2: 24 rolling sample set

Option 2 requires 24 start up samples per IBAA output. If you already have this data before the start of the protocol then you only need to take 2 random samples per IBAA output each month from 1 April 2026.

If you do not have historical sample data to use as start-up sampling:

• take 4 samples per month for the first 6 months to generate 24 start‑up data points
• then take 2 samples per month for the remaining 6 months (36 total samples in year 1)
• continue with 2 samples per month thereafter

If you have existing data from 2019:

• take 4 samples per month until you reach 24 data points
• then take 2 samples per month for the remainder of the year and until the protocol is reviewed (for example, if you already have 20 samples, take 4 samples in the first month)

Taking on new IBA waste streams

Before accepting new input wastes, you must ensure the waste producer has tested the proposed inputs. You must also assess the data to confirm the inputs will not compromise IBAA quality or introduce new hazards.

If you have a strong historic dataset, you can use it to exclude irrelevant hazards or identify hazards that must be regularly assessed, if evidence supports this. You must get this agreed with the Environment Agency first.

How to take your samples

This approach aligns with the ESA IBA protocol. It is designed to ensure sampling takes place throughout the entire production period of a load for each IBAA product stream, giving a representation of the whole load.

Step 1: Take incremental samples

You must take samples over one shift period, not exceeding 24 hours.

To produce a 200kg primary composite sample, collect 20 random incremental samples of approximately 10kg each from a chosen load of IBAA. You can do this using any of the following approaches:

• swipe samples across a conveyor over the time taken to produce one load, sampling multiple conveyors at the same time if a load comes from a blend of particle sizes
• spot samples from an excavator bucket during vehicle loading
• grid sampling of a flattened, prepared (mixed) stockpile
• face sampling during stockpile excavation or formation, avoiding the outer perimeter

Combine all 20 increments and mix well to create the 200kg composite sample.

Alternatively, you can collect approximately 20 tonnes of material by taking consecutive mechanical bucket loads from the falling stream, or by excavating the storage stockpile. Place the material against a barrier or wall, then mix mechanically by lifting a load with the bucket and slowly releasing it back onto the pile. Repeat 10 times, keeping the material in a single consolidated pile. Collect spadefuls from across the surface of a final bucket load and combine them to produce the 200kg sample.

Step 2: Use appropriate equipment

You must use tools at least twice the size of the largest particle to prevent exclusion of larger materials.

Step 3: Reduce and homogenise the sample

1. Place the 200kg composite sample in a clean, debris-free preparation area, using a hard-standing surface if possible.
2. Transfer the material into a cone-shaped pile 3 times using a hand shovel.
3. Divide the pile into 4 equal segments and discard 2 opposite quadrants, leaving approximately 100kg.
4. Create a new pile and divide into 4 quarters of 20kg to 25kg each.
5. Combine opposite quarters to produce one 40kg to 50kg laboratory sample and one 40kg to 50kg facility reserve sample.

Step 4: Contain and send the sample

1. Place each sample in suitable plastic containers, each no more than 15kg (approximately three 20 litre tubs for the lab sample).
2. Label all containers with site name, output name, date and time of collection.
3. Seal and send the laboratory sample to the testing house as soon as possible and within 48 hours.
4. Store the facility reserve sample where it cannot be damaged or contaminated.

Step 5: Complete documentation

Complete a sampling record, noting any specific features of the 200kg composite sample or the larger load it came from.

How to prepare samples at the laboratory

Step 1: Prepare the sample

Weigh the sample received and document any damage to containers, doming of sealed lids or other unusual observations on opening.

You must thoroughly mix the entire received sample and use coning and quartering to create a representative 20kg sub-sample. Keep the remaining 20kg as a laboratory reserve – label it and store it securely at 4°C, without any sample preparation, until analytical testing is complete.

Step 2: Dry the sample

You must dry the sample in multiple trays at 105°C until no further weight loss is recorded. Use this phase to calculate the bulk moisture loss. When the sample is finely ground, calculate a second moisture content to determine any residual moisture. Combine the 2 moisture contents to calculate the overall moisture of the sample received at the laboratory.

For samples requiring analysis of organic parameters (for example, hydrocarbons), you must dry these at 30°C to prevent loss of volatile organics. You must photograph the entire 20kg portion both wet and dry. After drying, combine all trays.

Step 3: Grind the sample

For compositional analysis, you must finely grind a 1kg sub-sample to sub-250µm. Reserve the remaining coarsely ground material until testing is complete.

You can remove inert non-grindable materials during crushing to protect equipment. Inert non-grindable materials include stones, ceramics, porcelain, brick and glass. You must record the weight of each removed fraction and photograph any removed items as evidence that the sample has not been compromised.

Removed material must not contain clinker or other incineration residues, which must be included in the test sample. Crush any clinker removed and return it to the sample.

If you remove copper forms where the specific surface area is greater than 0.67mm² per mg (equivalent to a copper sphere of 1mm in diameter or fine copper wire of a slightly lesser diameter) as part of non-grindable materials, you must weigh them and include them in back-calculations.

You must count and record items containing hazardous substances (for example, batteries) separately and include their contribution in back-calculated as-received concentrations. It is assumed that the content of ‘blown’ batteries is in the test sample.

You must only use the mass of inert removed fractions in weight correction for back-calculation. Return any non-inert items to the grinding process before creating the test sample.

Step 4: Replicate analysis

You should replicate determinations of copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) using aqua regia digestion (a mixture of nitric and hydrochloric acid used to dissolve metals) across 11 separate sub-samples. Report the mean value of these replicates for each sample.

Step 5: Resolve analysis problems

You must retest the sample if there is any quality assurance failure during sample preparation or analysis. If a result is unusually high or low compared with historic data, you must test the laboratory reserve sample. If a sample is lost or compromised, you must request the facility reserve sample from the IBAA producer.

Sampling and testing requirements

You must sample and test IBAA before mixing it with non-waste aggregate or with other waste aggregates.

The analytical laboratory you use should:

• operate a quality management system accredited by the United Kingdom Accreditation Service (UKAS)
• be specifically accredited for the following parameters as a minimum: lead, nickel, zinc, copper, pH and alkali reserve
• have suitable experience of preparing and testing IBAA matrices – you should confirm this with the laboratory

You can move IBAA from the production site before test results are available, subject to the requirements in the following sections of this guidance:

• ‘assessing your results’
• ‘interpreting your results’
• ‘if results confirm the waste is hazardous’

Calculating determinant concentrations

You must convert laboratory results (dry weight) to reflect the composition of your IBAA as it leaves your facility (wet weight, as-received basis).

Apply corrections for:

• moisture content
• any inert non-grindable materials removed during sample preparation
• the contribution of any hazardous-substance-containing items (for example, intact batteries) that were removed and must be included in back-calculations

This applies only to compositional data. It does not apply to pH, alkali reserve or leachability testing.

You must only use inert non-grindable components when correcting results to a wet-weight basis. If a laboratory reports inert and metal non-grindable fractions together as a single combined mass, you cannot use this data to calculate wet-weight concentrations.

Speciation

Speciation means identifying the exact chemical forms (or ‘species’) that heavy metals in your IBAA are present as, for example oxides, hydroxides, carbonates or metallic particles. Different species have different environmental behaviours and hazard profiles.

Speciation lets you apply refinement factors that reflect the proportion of each metal present in forms that contribute to hazardous properties. This gives a more accurate, site-specific assessment of IBAA rather than a worst-case assumption based solely on total metal concentrations.

If you have completed site-specific speciation agreed in writing with the Environment Agency, you can use those refinement factors.

Default interim refinement factors

If you have not yet completed speciation, or are waiting for Environment Agency approval of refinement factors you have submitted, you can use the following default refinement factors. But you must only use them for a maximum of 12 months until your own site-specific factors have been approved:

• copper hydroxide: 30%
• copper oxide: 35%
• copper metal particles: 35%
• zinc oxide: 35%
• zinc carbonate: 40%

The Environment Agency may change these default interim refinement factors at any time during the interim protocol, in consultation with industry, as more data becomes available.

Completing speciation

During the 12-month interim protocol period (1 April 2026 to 31 March 2027), you must complete full waste speciation for all sites you operate that do not have approved speciation. You must:

• carry out laboratory-based speciation of relevant metals using a recognised methodology
• produce site-specific refinement factors representing the hazardous fraction of each metal
• submit these factors, with supporting evidence, to the Environment Agency for formal agreement before using them

If you have not completed speciation within this period, you will no longer be able to use the default interim refinement factors after 31 March 2027. You must then apply a worst-case assessment approach in line with the WM3 waste classification technical guidance.

Hazardous property assessments

You can find guidance on assessing hazardous properties in Appendix C of the WM3 waste classification technical guidance.

The determinants you must assess as a minimum are:

• pH
• copper (Cu)
• nickel (Ni)
• lead (Pb)
• zinc (Zn)

The Environment Agency may require you to test and assess other determinants on a site-specific basis, if there are concerns.

You are responsible for:

• identifying all relevant hazardous substances
• staying informed of any new substances or changes to the classification of existing ones

If you identify additional determinants of concern in your ash, you must consider these and tell the Environment Agency. If annual full testing by your source incinerators identifies other determinants that may be of concern, you must include these in your testing.

Assessing your results

Option 1: 12 rolling sample set

You must use the most recent 12 sample results for each IBAA output to assess your waste for hazardous properties (the latest result plus the previous 11, including any results from an authorised accelerated sampling programme).

Your IBAA is hazardous if 3 or more exceedances (results above the hazardous waste threshold) occur within 12 consecutive samples, or if any single result is 4 times the hazardous waste threshold.

If your IBAA is classified as hazardous, you must:

• transfer it as hazardous waste to an appropriately authorised facility from the date you receive the result triggering the classification
• investigate potential causes of the exceedances and identify how to prevent recurrence
• carry out accelerated sampling at one sample per week for at least 6 weeks, giving a minimum of 6 results

You can only revert to non-hazardous classification once 6 weeks of accelerated sampling and the full most recent 12-sample cycle confirms a non-hazardous result.

Option 2: 24 rolling sample set

You must use the most recent 24 sample results for each IBAA output to assess your waste for hazardous properties (the latest result plus the previous 23, including any results from an authorised accelerated sampling programme).

Your IBAA is hazardous if 6 or more exceedances occur within 24 consecutive samples, or if any single result is 4 times the hazardous waste threshold.

If your IBAA is classified as hazardous, you must:

• transfer it as hazardous waste to an appropriately authorised facility from the date you receive the result triggering the classification
• investigate potential causes of the exceedances and identify how to prevent recurrence
• carry out accelerated sampling at 2 samples per week for at least 6 weeks, giving a minimum of 12 results

You can only revert to non-hazardous classification once 6 weeks of accelerated sampling and the full most recent 24-sample cycle confirms a non-hazardous result.

Interpreting your results

You must interpret results using the appropriate rules for your chosen sampling set option.

For both options, the analytical laboratory should have replicated determinations 11 times for each sample. Use the mean value of these results when assessing the hazardous properties of the sample.

If the analytical laboratory carried out 2 sets of 11 replicates on the same sample, you should average the adjusted reported concentration for all 22 replicates, unless the laboratory can justify that the first set was compromised. In that case, use only the second set.

You need to class a sample as an exceedance if any hazardous substance meets or exceeds the relevant hazardous property threshold. If the mean concentration falls below the threshold, it is a pass.

When assessing pH, a provisional pH threshold of 12.66 applies to this protocol. This will be reviewed at the end of the 12-month period using in-vitro data submitted by industry.

You must review each result individually and in the context of previous results. Record your findings and any actions taken.

You should use simple statistical trend analysis to identify:

• gradual or step changes in composition
• increases in the frequency of peaks or near-misses
• emerging patterns that may signal deterioration in IBAA quality

Compare average wet-weight compositional data (based on the mean of any replicate tests) with:

• the hazardous property concentration thresholds in the WM3 waste classification technical guidance
• the most recent nationally agreed guidance
• any other relevant evidence that refines the face-value assessment

A low relative standard deviation (RSD – a measure of variability across replicate results) indicates greater confidence in the analytical data. If a single replicate appears unusually high or low, or if RSD exceeds 100%, consider a retest on the laboratory reserve sample and discuss this with the laboratory.

If results confirm the waste is hazardous

You must classify IBAA as hazardous from the date you receive the result triggering a 3rd or 6th sample exceedance (depending on your chosen cycle), or a result that is 4 times the threshold. The following conditions apply:

• the result must be received within 25 working days of sample collection – if results take longer than 25 days, you must tell the Environment Agency immediately at wcrespond@environment-agency.gov.uk
• you must tell your supplying incinerators of any exceedance
• after a 2nd or 5th exceedance, you must investigate the underlying causes and take steps to prevent future exceedances

The Environment Agency will monitor results in real time throughout the year. If exceedances begin to trend higher than the existing dataset indicates, the Environment Agency may require you to classify IBAA from the date the sample was taken, rather than the date the result is received. A formal review will take place in September 2026.

Classifying IBAA from the date of result receipt only applies until the interim protocol is revised or withdrawn.

What happens next

After 12 months of sampling results have been received, a qualified and independent body must submit an assessment of the data to the Environment Agency on behalf of IBAA processors. The assessment must evaluate whether incoming IBA analytical results can reliably predict IBAA classification.

An industry-wide or site-specific assessment of pH must also be submitted at the end of the 12-month period to refine the IBAA-specific pH limit of 12.66.

The Environment Agency will then either move to a final protocol or revert to the WM3 waste classification technical guidance.

While this review is underway, processors can continue to use this interim protocol unless:

• the Environment Agency specifies otherwise
• a revised protocol is issued

The Environment Agency may withdraw support for the interim protocol at any time and require compliance with the classification approach in WM3.

If you need help

Email the Environment Agency at wcrespond@environment-agency.gov.uk if you have questions.

Published 7 May 2026