General guidance: pollution inventory reporting

Question 1

Understanding the pollution inventory

Accepted Answer

The pollution inventory provides information about the releases and transfers of substances from the industrial activities we regulate.

This helps:

provide the public with easy access to environmental information from industrial activities in their locality
protect the environment by providing information to assist us in developing regulation
government to meet its national and international environmental reporting commitments, such as the UK Pollutant Release and Transfer Register

Each relevant industrial activity must report annually the quantities of specified substances released to air, land, controlled waters, and in transfers off-site in wastewater. We also require details of the quantity, type and fate of wastes transferred off-site.

Question 2

How to report

Accepted Answer

You will need to report every year on discharges for the previous year. The reporting period is from 1 January to 28 February each year. For example, the reporting period to report your emissions for the 2023 calendar year is from 1 January 2024 to 28 February 2024.

If you operate multiple sites, you need to make a separate return for each site. If your site operates under various permits, you may need to submit a return for each permitted activity.

Make sure you only report the emissions from the permit you are reporting for. Do not add emissions from different permitted activities, or you might report a higher figure than your site has actually released.

We strongly recommend that you make your pollution inventory return online using the electronic data capture (PIEDC) system on our website. For most users, this is the quickest and easiest method.

If you have any problems using or gaining access to this system, please contact us on 03708 506 506.

If you cannot use the electronic system, you can use the Adobe Acrobat reporting form for your process. You can fill it in on your computer and send it to us by email or post. If you have submitted your return on PIEDC or sent a copy by email, you do not also need to send it by post.

Four forms are available – you only need to complete the one which is relevant to your operations. Use:

form PI-1: for EPR permitted sites
form PI-2: for intensive agriculture and landfill operators
form PI-3: for companies that only need to report to the UK-PRTR, such as mines and quarries
form PI-4: for companies reporting radioactive waste disposals, discharges and releases

You need to use the best data and techniques available to you, including any samples analysed and monitoring data. We do not require you to do additional monitoring and this guidance will help you to quantify releases where you do not have site-specific data available.

If you need help filling in the form, please speak to your local Environment Agency contact or:

email: pollution.inventory@environment-agency.gov.uk
call general enquiries: 03708 506 506 (Monday to Friday 8am to 6pm)

Guidance for specific sectors

You can find specific guidance for the following sectors with the pollution inventory reporting guidance on GOV.UK:

cement and lime
chemicals
chemical treatment of waste, including waste oil
combustion activities
ferrous and non-ferrous metals
food and drink
incineration
intensive farming
landfill
mining and quarrying
paper and pulp
refineries
waste transfer station

For radioactive substances, guidance is at the end of the pollution inventory reporting form for radioactive waste. If you submit your return using PIEDC, you do not also need to submit a form.

Low impact installations

If you hold a permit for a low impact installation, we don’t normally expect you to have any emissions above the reporting thresholds. To qualify as a low impact installation, you must meet strict criteria, as explained in the A1 installations: environmental permits guide on GOV.UK.

If a notifiable incident occurs you need to report the emissions for that year, as shown in the ‘Notifiable releases’ section of this guidance.

Reporting for partial years

If you have begun operating a newly permitted site during the reporting year, you should report emissions for the time you have been operational. For measured emissions, this is everything you have recorded. For calculated emissions, adjust the calculations so they apply only to the period you have been operational.

If a permit has been transferred to you during the reporting year, you should submit the pollution inventory return for the whole year under your ‘new’ permit reference.

Question 3

Completing your pollution inventory form

Accepted Answer

Part 1 – About you and your site

You must answer questions 1.1 to 1.6 as a minimum. Answering questions 1.7 to 1.9 is optional.

Radioactive substances only: your form is slightly different, and you only have 3 questions in this section. The numbering of the questions is different on your form. For 1.1, see question 1.2. For 1.3, see question 1.1.

Question 1.1 – Calendar year

Your report must be for the previous calendar year. For example, if you are reporting in 2024, you need to tell us about your emissions in 2023. Your answer to this question would therefore be ‘2023’.

Question 1.2 – Authorisation, licence or permit number

Please respond according to your current regulatory regime as follows:

use the original permit number (in the format AB1234XY) if you are a permitted site
use the pollution inventory reference number if you are not a permitted site

Please email pollution.inventory@environment-agency.gov.uk if you are not sure.

Question 1.5 – NACE and NOSE-P codes

Please select the correct 4-figure NACE code and the 5-figure NOSE-P code from the pollution inventory reporting codes list.

This question does not apply if you are only reporting radioactive substances.

Question 1.6 – UK-PRTR Codes

Add in the UK-PRTR code (formerly E-PRTR code) for your main activity. These are available in the pollution inventory reporting codes list. If appropriate, you can include additional codes for other activities that you carry out.

This question does not apply if you are only reporting radioactive substances.

Parts 2 to 5 – Releases and Transfers

Parts 2 to 5 require you to report annual mass releases of specified substances to air, land and controlled waters, and off-site transfers in wastewater from the ‘reporting unit’ specified in Part 1.

If you are only reporting radioactive substances, there are only 4 parts. These are annual releases of specified or grouped radionuclides to air, sewers, and controlled waters in radioactivity units of Becquerels (Bq) or multiples of Bq. The reporting of transfers of radioactive waste is not required. For more help, refer to the guidance at the end of the pollution inventory reporting form for radioactive waste.

You must report all applicable pollutants, whether or not they are specifically detailed on your permit.

The pollution inventory reporting process for emissions to air and water follows 5 basic steps.

Identify relevant pollutants for the pollution inventory from permitted activities. Report non-relevant pollutants as ‘n/a’ (not applicable). Consider both direct and fugitive emissions.
Identify emission sources.
Allocate relevant pollutants to sources.
Quantify emissions by using the guidance in this document.
Complete the pollution inventory return with either an actual value, or you can enter ‘brt’ (below reporting threshold) where applicable.

You should use an appropriate release estimation technique (RET) to quantify your emissions.

There are 4 types of RET:

sampling or direct monitoring
emission factors
fuel analysis or other engineering calculations
mass balance

Depending on the site, pollutant, or process, any of the above techniques may be the most appropriate. You should understand the factors that lead to the selection of the most appropriate RET and be able to justify why the technique has been selected. You should always select the RET based on the application for which it has been designed.

Some mandatory RETs exist, such as when reporting emissions under the UK industrial emissions best available technique (BAT) regime or in accordance with permit conditions. An example is the reporting requirement under the UK Emissions Trading Scheme (UK ETS) for greenhouse gases.

If there are no mandatory or industry methodologies, you should use site-specific data. This could be from monitored emission concentrations or mass balance techniques where appropriate. Ideally, measured emission concentrations should be based on data obtained using appropriately certified equipment or accredited services. You should normally use continuous monitoring data in preference to data from periodically sampling.

Where emission factors are used, you should give preference to site-specific emission factors rather than those developed from other representative plant. To develop a site-specific emission factor you will need to relate the level of emissions to an activity within the process. This is normally achieved by sampling and monitoring, from the manufacturer’s information or by calculation.

Some emissions from a process will have more impact on the environment than others. You need to concentrate efforts, and use the most accurate RETs, on those emissions that have associated emission limit values in a permit and also on those which exceed the pollution inventory reporting threshold values the most.

The 4 RETs relate principally to representative operating conditions. Emissions resulting from significant operating deviations (for instance failure of abatement plant) or accidental events, such as spills, also need to be estimated. In the case of air emissions from spillage events, it may be necessary to make an estimate of the amounts of substances released as vapour. For all spills you should report the net emission – that is, the quantity of the substance spilled minus the quantity recovered or consumed during clean-up operations.

If an emission factor or other emission estimation technique is not available, please email pollution.inventory@environment-agency.gov.uk or contact your local Environment Agency officer.

Part 2 – Releases to air

In this context, ‘air’ includes both the inside and outside of a building.

Make sure you do not double count when you are quantifying the amounts released from a given point. For example, if you have vapours coming off a process inside a building which are then collected and discharged through a stack, only count the emissions from the stack. If you have some collected vapours and some which are not collected but escape through doors and windows, you will need to count both.

Part 3 – Releases to land

This only applies to waste that is subject to the disposal operations ‘land treatment’ or ‘deep injection’. If waste is treated in this way, substance specific releases must be reported by the operator of the installation producing the waste, regardless of the disposal location. You do not have to report accidental releases of substances onto the soil of the installation, for example, as spillages.

Part 4 – Releases to controlled waters

These include:

groundwaters (G) – any waters contained in underground strata
rivers and inland waters (R) – this includes surface fresh waters, that is those inland surface fresh waters which are not part of, and are upstream of, an estuary
estuary (E) – the transitional area at the mouth of a river between fresh water and coastal waters – the UK has established estuary boundaries and we hold maps of these
sea (S) – coastal waters up to 3 miles from the coast with respect to a landward baseline – we hold maps of this baseline

Part 5 – Off-site transfers in wastewater

This comprises all relevant substances transferred to wastewater treatment plant via sewer or other means, for example by tanker.

As with air emissions, make sure you do not double count. For example, if you transfer effluent within your site, or pre-treat it before discharge to sewer, only count the final discharge from the site.

Parts 6 and 7 – Waste transfers

This section does not apply if you are only reporting radioactive substances.

Within-country waste transfers

You must classify wastes using the:

European Waste Catalogue (EWC) 6-digit codes
relevant Waste Framework Directive [disposal or recovery (D&R) codes - see the pollution inventory reporting codes list for these

There is no reporting threshold for hazardous wastes, which are indicated by an asterisk in the EWC. For all other combinations of EWC and D&R codes, a reporting threshold of 5 tonnes applies.

Report the annual tonnages of wastes arising from process-related activities and transferred off-site for disposal or recovery. Exclude liquid wastes transferred via sewer or other means to wastewater treatment plant (report these as substance-specific off-site transfers in wastewater).

Ensure that waste is described accurately as being sent for recovery or disposal. Recovery of waste includes recycling, re-use, processing to extract secondary raw materials, or use primarily as a fuel to generate energy (co-incineration).

Disposal covers operations other than recovery. For example, this could be waste to landfill, or burning of waste in an incineration plant.

Complete the relevant 6-figure List of Wastes (LOW) Regulations codes in the first column in the format XX XX XX.
Complete the relevant Waste Framework Directive Disposal or Recovery (D&R) codes in the first row.
Enter waste tonnages or ‘brt’ as appropriate. There is no need to insert ‘n/a’ in the boxes where no waste is transferred off site.

Any transfer of waste off-site to a third party is covered by the duty of care provisions of the Environmental Protection Act 1990. This includes the requirement to describe the waste and record the quantity. You should use data generated in compliance with duty of care requirements to complete the pollution inventory return. The only additional information that is required in reporting off-site waste transfers to the pollution inventory is the appropriate Waste Framework Directive D&R code.

You should not report wastes that are temporarily stored on site by yourself, as these are not classed as off-site waste transfers for the pollution inventory return. However, waste transferred to third parties (even if stored on your site) should be reported.

Overseas waste transfers

If you have sent any hazardous waste overseas for disposal or recovery, you need to tell us in Section 7. You will have reported this already in Section 6, but we need more details for overseas transfers.

Part 8 – Resource efficiency

You no longer need to report resource efficiency data as part of your pollution inventory return. We have removed this from PIEDC. If you use the paper form and fill in this section, it will not be used for any purpose.

For some sectors, there may be a specific benefit in continuing to collect resource efficiency information. Where this is the case, we will work with you and trade associations to find other options for collecting this data. For example, we might ask you to use trade association corporate and social responsibility reporting schemes.

Question 4

Reporting conventions – how to complete the table

Accepted Answer

Total releases (including notifiable releases)

You must report your total annual mass releases or transfers for each specified substance and each medium in the ‘total releases’ column. Include point source, fugitive, and any notifiable releases in this figure.

Enter a release value, ‘n/a’ or ‘brt’ in the ‘total releases’ column as appropriate.

Release above reporting threshold: When the annual release exceeds the reporting threshold, enter the total annual mass released or transferred.

Below reporting threshold: If you have emitted a substance, but the quantity of the annual release or transfer is below the reporting threshold, you can enter ‘brt’ instead of a value. We encourage you to enter the actual value if available, even if it is ‘brt’ to provide us with a more complete picture of industrial emissions. Your local Environment Agency contact may have asked you to only record actual values, not ‘brt’ – if so, you should do this.

Not applicable: If no release or transfer of the substance occurred in the reporting year to that medium, you do not need to enter a value and should enter ‘n/a’ instead.

Point source emissions

These emissions are from a specific location from a single point source. For example, when they are exhausted via a chimney, stack, or vent.

These are also known as channelled emissions, which are defined as “emissions of pollutants to air through an emission point such as a stack” (Official Journal of the European Union 12.12.2022 L 318/157).

Abatement equipment, such as scrubbing units and fabric filters, can be incorporated into the exhaust system prior to discharge to atmosphere. This might reduce your point source emissions.

Diffuse emissions

Diffuse emissions are defined as non-channelled emissions to air. Diffuse emissions include fugitive and non-fugitive emissions.

These are emissions that are not released from a point source such as a chimney. Leaks from valves and flanges are examples of fugitive emissions.

Fugitive emissions to air include leaks caused by loss of tightness of equipment which is designed or assembled to be tight.

Fugitive emissions can arise from:

moving equipment, such as agitators, compressors, pumps, and valves (manual and automatic)
static equipment, such as flanges and other connections, open-ended lines, and sampling points

Non-fugitive emissions are diffuse emissions other than fugitive emissions.

Example sources of non-fugitive emissions are:

atmospheric vents
bulk storage
loading or unloading systems
open gutters
sampling systems
sewers and water treatment plants
tank venting
vessels and tanks (on opening)
waste

As with other releases, you should use an appropriate release estimation technique (RET) to quantify your emissions. These need to be added to your total release value for the relevant substance.

You only need to report fugitive emissions that leave the site to the PI. For example, you should report vapour emissions that may have dispersed. Such substances may be methane or non-methane volatile organic compounds (VOCs) that escape from your plant. You should not report contained spills.

Notifiable releases (as defined in Part B of your permit)

These are unplanned and unauthorised releases of a particular substance or substances to the environment. They may result from an emergency, mis-operation, accident, or plant failure such as a failed pressure relief valve on an aerobic digestion plant.

The permit or authorisation requires you to provide us with a specific notification, followed by specific information on the releases. If they were made during the reporting year, the amounts released should be quantified and detailed in the ‘notifiable releases’ column and included with any other releases in the ‘total releases’ column. You should estimate the mass lost to each release medium.

There is no reporting threshold for this category, so if none has taken place use the ‘n/a’ designation.

Case studies for notifiable releases

Plant failure at Anaerobic Digestion plant: A blockage in the sludge outlet from an Anaerobic Digestion tank resulted in sludge entering and blocking the gas outlet. The subsequent build up in gas pressure caused the pressure release value to operate. Approximately 1600m³ of biogas was vented over a 4-hour period whilst the blockage was cleared.

You calculate that 750kg of methane was lost to air as a result of the failure. Report this loss to air in the ‘Notifiable releases’ column.

Fire: An accidental fire in a solvent recovery plant results in the combustion of 2 tonnes of acetone. Report this loss to air in the ‘Notifiable releases’ column. Use emission factors to estimate pollutant releases to the atmosphere during the incident.

Power outage at a gas producing site: All the gas control measures and backup generator to the flare fails at a gas producing site such as a landfill or anaerobic digestor. The flare didn’t operate so gas built up and couldn’t be used or flared, so it vented for 6 hours. The site produces 1100m³ per hour. You calculate that 6,280 Nm³ of biogas or landfill gas was generated and lost through venting over 6 hours because it had nowhere else to go. At your site your gas quality was known to be 55% biomethane at a normal operating temperature of 40° Celsius. Report this loss to air in the ‘Notifiable releases’ column.

Further calculations for this example, and conversion factors for how to estimate your notifiable releases of biogas, is in our technical guidance and equations.

All instances need to be aggregated in the submission but recorded separately.

Codes for methods used to determine releases

Enter the code that corresponds to the method you used to determine the largest proportion of the annual releases. The 3 codes are:

Measurement (M): Based on standardised or accepted methods. You may need additional calculations to convert into annual releases. Continuous release monitoring will yield the most accurate figures.

Calculation (C): Based on nationally or internationally agreed estimation methods and emission factors that represent the industrial sectors. This covers activity data such as fuel used, production, mass balance approaches and published references. You must ensure you are using the most up to date methods and emission factors for your sector.

Estimation (E): These are non-standardised and are based on expert judgement. Contact your local Environment Agency officer to discuss estimation methods if required.

Detailed release determination methods: If you enter methods M or C you will need a specific determination method code. See the pollution inventory reporting codes list for method codes. This is not required if ‘E’ is selected.

Worked examples – how to obtain method codes

Example 1: The annual release of a substance to air from a plant was determined purely from monitoring data of stack releases, and there were no other sources of this substance to air from the plant. The data are measurements, so enter ‘M’.

Then select the appropriate detailed measurement method from the pollution inventory reporting codes list.

Example 2: The annual release of a substance to air was determined from 3 processes by different approaches:

30% of the total from measurement (releases from a stack)
15% of the total by estimation (fugitive releases)
55% of the total by calculation (releases from vents)

The greatest proportion of the total annual releases to air was determined by calculation – enter ‘C’.

Then select the appropriate detailed measurement method from the pollution inventory reporting codes list.

Limit of detection (LOD)

If the best available information indicates that a substance is not released from your process, report ‘n/a’ for that substance.

Where a substance may be released but at a concentration that is below the limit of detection, you also need to report ‘n/a’ unless an alternative release estimation technique, such as mass balance, produces an applicable result. By limit of detection, we mean the lowest concentration which can be measured by the analytical method prescribed in the permit, or another method approved by us.

We recognise that there may be circumstances where some analyses in a series do not detect a substance, but others do.

If no more than 5% of the readings show a positive value, and the values obtained are not more that 20% above the accepted limit of detection, you can treat them as if they were also reported as below the limit of detection.

In any other case, use the values obtained. Assume that where the substance is reported as not detected, it is present at 50% of the LOD. In these cases, to determine the mass emission, you need to multiply each concentration by the total flow during the period that the measurement relates to. That is, report those measured above the LOD as measured, and those measured at below the LOD as half of the LOD.

In some cases, we may have agreed a different methodology with you for a particular substance or process. If so, use this in place of the procedure above.

If this methodology gives you a positive result that is below the reporting threshold, it should be reported as ‘brt’ rather than ‘n/a’. You can report the actual value instead of ‘brt’ if available. In some cases, we may have requested that you do this.

Mass units and significant figures

Quote all releases in kilotonnes ‘kt’, tonnes ‘t’, kilograms ‘kg’, grams ‘g’ or milligrams ‘mg’ per year with 3 significant figures.

The unit of radioactive waste disposal is in Becquerels (Bq) or multiples of Bq.

Make sure that you are reporting with the correct units.

Rounding to 3 significant figures does not refer to the statistical or scientific uncertainty but provides a common standard for all reported data. When rounding the figures, the numbers 5 and higher should be revised up and 4 or lower should be revised down.

Examples of rounding raw data to 3 significant figures are as follows.

Original release	Release reported to 3 significant figures
0.0000123421	0.0000123
1.23417	1.23
12	12.0
123.443	123
123,626,789	124,000,000

Reporting substances – general principles

For inorganic and organic substances, you should report the total mass of the specified substance.

For metals and compounds, you should convert the mass of each relevant compound to the mass of the metal it contains.

For other substance groups you should normally report the total mass. Be aware that there are some specified exceptions (for example dioxins and furans).

There’s pollution inventory guidance on reporting specific substances and substance groups in the:

sector-specific guidance
technical guidance and equations for reporting

Radioactive substances

For radioactive substances, please refer to the guidance at the end of the pollution inventory reporting form for radioactive waste.

Question 5

Monitoring techniques and emission factors

Accepted Answer

Guidance on monitoring techniques

If you are using source monitoring data to generate annual mass releases, you can check best practice from our series of monitoring technical guidance:

A range of documents on good monitoring practice have been published by:

the International Standards Organisation (ISO)
the European Committee for Standardisation (CEN)
the British Standards Institute (BSI)
other organisations including the German Institute for Standardization (DIN) and American Society for Testing and Materials (ASTM) standards organisations

Question 6

Other sources of information for emission factors and release determination

Accepted Answer

Releases to air (in priority order for UK use)

The National Atmospheric Emissions Inventory (NAEI)

This includes estimates of releases of numerous atmospheric pollutants. It is useful for estimating releases from industrial combustion processes and for VOC speciation.

Defra’s environmental reporting guidelines

This guidance is written to help companies comply with the Streamlined Energy and Carbon Reporting Regulations, including greenhouse gas reporting. This links to reporting conversion factors for each calendar year.

Atmospheric Emission Inventory Guidebook

This is maintained by the United Nations Economic Commission for Europe’s Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe programme (UNECE EMEP). It contains chapters for specific source sectors, where all available emission factors and calculation methods are collected. It is a useful source of emission factors which are not available from the NAEI.

Intergovernmental Panel on Climate Change (IPCC)

The IPCC has produced guidelines for the establishment of emission inventories of greenhouse gases within its National Greenhouse Gas Inventory Programme (NGGIP). The revised IPCC guidelines for national greenhouse gas inventories contain emission factors and release estimation methods for all sectors as defined in the United Nations Framework Convention on Climate Change. The IPCC also developed a report on ‘Good practice guidance and uncertainty management in national greenhouse gas inventories’.

United States Environmental Protection Agency (EPA) Office of Air Quality Planning and Standards

The US EPA maintains a comprehensive website where all material on emission factors and release estimation methods in the US can be viewed and, in many cases, downloaded. In general, emission factors from these sources should only be used in the absence of appropriate UK or European values.

Environment Australia

This gives Australian Emission Estimation Technique industry manuals.

Releases to water

OSPAR Commission

This gives information on the releases and pollutants to water covered by this agreement.

Norwegian Environment Agency

The (no longer operational) Norwegian Pollution Control Authority project ‘Harmonised quantification and reporting procedures for hazardous substances (HARP)’ contains information on the releases and pollutants to water.

Other sources of information

European IED and BREF documents

The EU Integrated Pollution Prevention and Control (IPPC) Directive, 1996, stated that the conditions of permits that member states issue on Annex I activities must be based on best available techniques (BAT) to achieve a high level of protection of the environment as a whole.

BAT reference documents (BREFs) were produced, and they contain information on:

production processes and techniques
current release levels
release reduction measures and techniques in the determination of BAT

The IPPC was repealed by the Industrial Emissions Directive (IED) 2010 and BREFs were adopted under the IED.

Existing EU BAT conclusions continue to have effect in the UK through the EU Withdrawal Act 2018. They are available in BREFs.

The Environment Agency is developing a series of UK BAT conclusions relevant to each EPR or IED sector and sub-sector.

UNEP: United Nations Environment Programme

Has an ‘Inventory on information sources on chemicals’.