Guidance

Waste transfer station: pollution inventory reporting

Updated 21 August 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

If you operate a waste transfer station as a Part A1 installation, you must submit data to the pollution inventory. The Environment Agency will have sent you a notice explaining this when your environmental permit was issued.

The ‘general guidance’ available in the pollution inventory reporting guidance gives information that applies to all business and industries. It explains what the pollution inventory is and how to report.

This guidance gives information specific to operators of waste transfer stations. It will help you to:

• identify the pollution inventory substances relevant to your operation
• estimate the annual mass of such substances released to air, sewers, and controlled waters

The guidance is based around unit operations likely to take place at facilities falling under Section 5.3 - Part A1(a) and Part A1(b) of Schedule 1 of the Environmental Permitting Regulations (EPR) and primarily involving hazardous waste disposal.

On our website, you can find pollution inventory reporting guidance for other waste treatment activities. These include:

• ferrous and non-ferrous metals
• landfill
• incineration activities
• chemical treatment of waste
• combustion activities

Description of operational activities

The following sections provide a summary of:

• different activities that commonly occur at waste transfer stations
• the likely sources of emissions associated with these

If you operate a transfer station without bulking or processing activities

Site activities:

• acceptance of mixed items
• repackaging mixed items into larger containers for onward shipment without decanting the waste

Likely sources of emission are:

• accidental breakage of waste containers
• emissions associated with any fuel used at the site

If your site undertakes bulking and storage

Site activities:

• acceptance of mixed items
• transfer of material with similar properties into bulk containers for onward disposal
• disposal of original containers to landfill or recycling

The bulk containers may be drums, intermediate bulk containers (IBCs), or tanks. There may be several types of bulking and storage activity, such as:

• laboratory smalls to drums
• drums to IBCs
• tanker loads to storage tanks

There is a large range of emissions from this type of site. Likely sources of emission are:

• accidental damage
• emissions from fuel use at the site and each transfer of waste
• processing of the original container can generate liquid and vapour emissions

All transfers of material can cause discharges. These may be:

• small spills and splashes from manual decanting
• releases from pipe couplings and valves
• residues from washing tankers and containers
• displacement of air rich in solvent vapours when filling and emptying tanks and tankers

The wide range of possible emissions to air, sewer and controlled waters must be estimated in relation to the range of activities and wastes handled at a particular site.

Abatement systems to control most of these emissions are available, but these are not used consistently across the UK. You need to assess the effectiveness of your own abatement systems.

Sites associated with adjacent treatment or recycling plant

Sites next to a treatment or recovery plant might separate or decant wastes suitable for treatment in that plant, and bulk other wastes for disposal elsewhere.

The same range of emissions as previously described is possible, but it is common for the entire drainage system at the transfer station to be linked to the adjacent treatment plant. No emissions to sewer or controlled water from the transfer station itself should happen under these circumstances. You should report emissions from any on-site treatment plant as part of the total site emissions.

Some atmospheric emission control systems for the main treatment plant may be extended to cover storage units at the transfer station. The emissions from this element of the storage are reported as part of the total site emissions.

Other activities you may carry out

Some transfer stations undertake additional treatment operations, usually physical processes, on a portion of the waste stream. These might be solid and liquid separation, oil and water separation, or waste conditioning processes.

Each of these will generate specific emissions and each needs to be assessed. These are not covered in the following discussion, so you need to make your own assessment.

How to identify the important waste streams

In principle, small quantities of every material handled at the site will be released. In practice, the risk of emission will be proportional to the amount of each material handled.

The following approach is reasonable for most sites and provides a simple basis for justifying your declaration to the pollution inventory.

1. Make a list of the 20 most common waste types handled at your site that have been decanted into larger containers or bulked into tanks. (Larger sites may need to review more than 20 wastes, smaller sites may only need to look at fewer.)
2. Determine the average content (analysis) for these wastes and the annual tonnage - make sure that this includes your bulk solvent streams.
3. Identify which of these contain substances that are relevant to the pollution inventory for emissions to water or air.
4. Identify any other species relevant to the pollution inventory for which you have monitoring data.
5. Consider the type of site activity that affects these waste types (decanting, washing containers, and so on).
6. Where you do not have monitoring data to calculate the emission, undertake emission estimations on these activities (see sections below) and generate data to complete your declaration.
7. Review the other species on the pollution inventory declaration form. If you are aware that there are significant emissions of other species, acknowledge these as ‘brt’ (below reporting threshold) or you can provide an actual value if available.

Quantifying emissions to air

Most of the atmospheric emissions from your site will be associated with transferring and bulking volatile organic compounds (VOCs), in organic wastes and primarily solvent wastes. These are the key emissions to quantify. Other waste streams that are known to contribute to atmospheric emissions at transfer stations are ammonia wastes, strong acid wastes, and powders or dusty wastes.

The following substances are the most likely to be released to air:

• ammonia (NH₃)
• hydrogen chloride (HCl)
• particulate matter
• strong acids
• volatile organic compounds (VOCs)

Sources of emissions to air

Transferring organic wastes will result in VOC emissions to atmosphere unless there are substantial abatement control systems. Similar emissions are expected from the transfer of ammonia wastes, and from strong acid wastes. Other emissions to atmosphere will occur at the same time, but the quantities will generally be minimal for most materials.

Sites handling powders and wastes giving rise to dusts (fly ash, for example) will release particles to atmosphere. These may need to be considered where there are large quantities involved. Common abatement systems are fitted on venting systems for tanks, and to reduce solvent losses to atmosphere due to displacement when filling tanks and tankers. Sites handling dusty wastes may have specific hoods, filters, and extraction systems for these.

We have listed a range of activities at transfer stations that may cause substantial emissions. From the earlier descriptions and your own knowledge, consider which of these apply to your site, the type of waste stream associated with each, and the abatement or mitigation systems you have in place.

Accidental emissions are not covered and would require a separate assessment. You should report these as ‘Notifiable emissions’ and add into the ‘Total emissions’ figure:

• filling bulk storage tanks by road tankers: displaced air and losses from transfers may lead to release of VOCs
• storage in bulk tanks: vented material may lead to release of VOCs
• emissions from pipes and pumping systems: all losses may lead to release of VOCs
• gravity and vacuum emptying of drums, IBCs, and other containers to bulk tanks: displaced air and losses from transfers may lead to release of VOCs
• storage and handling of empty IBCs: storage may lead to release of VOCs
• storage and handling of empty drums and other similar containers: crushing activities may lead to release of VOCs
• maintenance of equipment: tank cleaning and washing may lead to release of VOCs
• planned evaporation of volatile liquids: evaporation may lead to release of VOCs

Filling of bulk storage tanks by road tanker

You will need to calculate the atmospheric VOC emissions due to the venting of vapour contained in the receiving vessel. Where the receiving tanks are fitted with emission abatement equipment, for example carbon adsorption, the emissions from this activity are likely to be minimal and can generally be ignored.

For calculations, we assume that the air displaced from the storage tank is saturated with vapours associated with the organic liquid mixture in the tank. The mole fraction of each vapour in the displaced air can be calculated using Equation 1.

Equation 1: y = x (VP / P)

Where:

• y = vapour mole fraction of substance in displaced air
• x = liquid mole fraction of substance (x = 1 for waste solvent containing one component).
• VP = vapour pressure of component in the tank (kPa): this can be obtained from material safety data sheets or standard chemical engineering reference books
• P = system pressure (kPa): in most cases, such as for open reactors, this will be ambient pressure (101.3kPa) (reference Environment Agency, Emission scenario document on transport and storage of chemicals

Having determined ‘y’ for each vapour present, divide the volume of waste solvent added in litres (equals volume of air displaced) by 24.436 (assuming a liquid temperature of 25°C). This will give you the number of moles of displaced saturated air. Multiply this figure by each value of y to determine the number of moles of each waste solvent vapour emitted. Multiply the resulting figure by the appropriate molecular weight to determine the mass of each substance emitted.

Gravity and vacuum emptying of drums, IBCs, and other containers to bulk tanks

There are two elements to this emission:

• the displacement of vapour saturated air in the container
• fugitive losses during transfer

Equation 1 can be used for the displacement calculation, but there is no simple method available for the fugitive losses due to transfer. At present, these are covered by estimating the losses associated with the reject container, see below.

Storage and handling of empty IBCs, drums, and smaller units

This section is about emissions to atmosphere from solvent residues in containers. Aqueous wastes and residues are considered in the section Quantifying emissions to water.

Most emptied IBCs will be cleaned for reuse or onward sale. The cleaning process typically involves evaporating residual solvents and washing the container. Metal drums are typically crushed and sold for recycling, although some are reused or sent to landfill. Smaller containers usually go to landfill.

Some waste transfer stations have drainage areas where ‘emptied’ drums are left upside down to drain over a grid and sump. The tonnage of solvent collected in this, or similar, manner should be deducted from the calculations below. Sites with a liquid collection sump beneath the drum crushing unit will tend to evaporate solvents from the drum before crushing to avoid explosion.

After decanting, ‘empty’ solvent containers are left to vent to atmosphere. This may be in a separate area of the site, or simply in the skip of waste for landfill.

To estimate emissions, you should assume that 1% of the container volume is left as liquid residue in 205 litre drums and smaller containers, and 0.5% in IBCs. There may be sludge in addition to this.

Total annual emissions from IBCs will be:

Equation 2: Emissions = 5 x N litres

Where:

• N = number of 1,000 litre IBCs handled per annum

Total annual emissions from smaller containers will be:

Equation 3: Emissions = (V x 0.01) x N litres

Where:

• V = volume of container (litres)
• N = number of containers per annum

In both cases, the mass of emissions can be calculated from the specific gravity of the liquid.

Transfer stations that bulk small volumes of organic solvents may find it hard to quantify the number of containers and the wide range of incoming solvents. It may be easier to consider emissions related to the average concentration of the mixed wastes leaving the site. This is likely to be one of the ‘top 20’ waste streams at your site.

Total annual emission can be calculated using equation 4.

Equation 4: Emissions = Z x (0.01 – (0.00005 x Y)) kg

Where:

• Z = the outgoing solvent waste stream in kg per annum: this is created by bulking from IBCs or smaller containers
• Y = the percentage received in IBCs. For most sites, Y will be 0% or 100% for given waste streams. Otherwise, use your best estimate.

Using the average concentration of the outgoing solvent stream, calculate the emissions for specific species as a proportion of Z.

Quantifying emissions to water

If all surface water drainage and liquid waste from sumps, crushers and washing areas go to an on-site treatment plant prior to discharge to controlled waters or sewer, you do not need to declare water emissions for this part of the licensed activity. You do need to report any emissions to controlled waters or sewer from the treatment plant.

For other transfer stations, you can use the water emissions estimation approach outlined below.

The following substances are the most likely to be released to water:

• chlorides (Cl)
• copper (Cu)
• nickel (Ni)
• nitrogen (N)
• phosphorus (P)
• total organic carbon (TOC)
• xylene and toluene
• zinc (Zn)

References to sampling methods are included in the pollution inventory general guidance mentioned at the beginning of this guidance.

Unless you are handling biocide contaminated wastes it is unlikely that the following substances will be emitted. You will report these substances as ‘n/a’ for all relevant media unless you know better for your site. Common biocides are:

• aldrin
• atrazine
• brominated diphenylethers
• DDT
• dichlorvos
• dieldrin
• endosulfan
• endrin
• hexachlorobenzene
• hexachlorocyclohexanes
• nonylphenols
• PCBs
• pentachlorophenol
• simazine
• tributyltin compounds
• trifluralin

Sources of emissions to water

Most sites will have a continuous, but small, discharge of waste to the site base from:

• drips
• splashes
• crushing residues
• pipe connections
• oil leaks
• other, similar sources

These will be washed to the surface waste collection points by rainwater and site cleaning.

Almost all hazardous waste transfer stations have a secure base laid to drain rainwater and liquid or solid spills to one or more liquid tanks or interceptors. There may be separate drainage systems and sumps to isolate specific areas of the site where waste is handled and bulked to contain possible spills and protect surface water drainage from contamination. These will reduce liquid emissions.

The surface water drainage may be discharged to sewer, to controlled waters, or to an adjacent treatment plant. Discharge consents to sewer or controlled waters will reflect some of the risks associated with the transfer station and specify monitoring requirements.

The most common materials to be bulked at transfer stations are:

• aqueous organic wastes
• caustic solutions
• dilute acids (often from metal treatment)
• non-halogenated solvents
• oils

The discharge to sewer is almost certain to contain:

• chloride
• nitrogen
• total organic carbon
• xylene (if you are bulking non-halogenated solvents)
• zinc

We have listed a range of activities at transfer stations that may cause substantial emissions. From the earlier descriptions and your own knowledge, consider which of these apply to your site, the type of waste stream associated with each, and the abatement or mitigation systems you have in place.

Common sources of emissions to water (including both controlled waters and sewers) are:

• filling of bulk storage tanks by road tankers: losses from transfers
• emissions from pipes and pumping systems
• gravity and vacuum emptying of drums, IBCs, and other containers to bulk tanks: losses from transfers
• storage and handling of empty IBCs: washing activities
• storage and handling of empty drums and other similar containers: crushing and washing activities may lead to liquid and solid releases
• washing of road tankers: effluent releases
• maintenance of equipment: tank cleaning and washing may lead to liquid and solid releases

Accidental emissions are not covered and would require a separate assessment. You should report these as ‘Notifiable emissions’ and add into the ‘Total emissions’ figure.

Emissions for washing containers and tanks

Liquid emissions may arise from washing and processing containers prior to their reuse, recycling, or disposal. You might also get emissions from washing road tankers.

To estimate these emissions, you can use Equation 5. Assume that the residual material in each type of container after emptying is 0.5% of the volume, and that all this material is washed to sewer.

Equation 5: Emissions = V x 5 kg

Where:

• V = the volume of the container or tanker (m³)

This uses a uniform density of 1 tonne per cubic metre, on the assumption that this process will occur with aqueous waste streams.

In general, volatile residues from containers of solvent waste are evaporated directly to atmosphere rather than washed to sewer.

If the relevant species are covered by your site monitoring programme, this will provide an alternative source of data to estimate the annual mass of emissions.

General emissions from fugitive leaks and spills

The following approach gives an estimate of emissions to water for sites with contamination of surface water caused by small fugitive emissions.

1. Review your list of the 20 most common wastes and which species are relevant to the pollution inventory for emissions to water.
2. Identify the substances on the pollution inventory list for which monitoring data are available and calculate annual emissions for these based on discharge volumes and analytical results.
3. For substances which you don’t have monitoring data for, make a best estimate based on your calculated volumes and other results.
4. Assume that emissions of the remaining substances from your top 20 will be below the reporting threshold and enter these as ‘brt’ on the emission declaration form. We encourage you to enter an actual value if available.
5. Consider whether you are decanting wastes containing nitrogen, phosphorus, chloride, or organic carbon - if so, ensure that the boxes for TOC, total nitrogen, total phosphorus, and chloride are recorded with a value, or as brt.

How to quantify emissions from other processes

We have indicated the species most likely to be emitted from this type of waste management site, and this will help you complete your declaration.

Please remember it is your responsibility to use the best data and techniques available to you to work out emissions from your operation. This guidance relates to a standard waste management facility undertaking a single operation with limited waste streams. Many sites undertake a range of activities and process a wide variety of wastes.

Consider whether you are doing additional operations at your site, or processing unusual waste types that will add to emissions. Some of these might be:

• transfer and bulking powders or separating, grinding, crushing or trommelling of mixed non-hazardous wastes with potentially high discharges of particles to atmosphere
• crushing oil filters and separating them into a solid metal fraction and a liquid oil fraction - if not undertaken in controlled conditions, there will be an oil mist discharge to atmosphere including PAHs and VOCs
• using waste solvent to clean other equipment, resulting in discharges of the solvent to atmosphere
• turning, grinding, or otherwise exposing to atmosphere, solvent sludges or solvent contaminated wiping cloths prior to landfill, resulting in solvent emissions to atmosphere
• on-site combustion processes resulting in emissions of CO₂, SO₂, NOx, VOC, CO, PM10 and PAH - emissions can be estimated by multiplying annual fuel use by appropriate emission factors such as those given as Table 1

Table 1: Combustion emission factors (kg/tonne fuel, unless otherwise specified)

Substance	CO2	SOx	NOx	NMVOC	CO	PM10	PAH
Residual fuel oil	3,112	47.4	7.54	0.125	0.5	2.85	0.15 (g/te fuel)
Distillate (gas) oils	3,142	3.6	3.46	0.0875	0.06	0.2	0.15 (g/te fuel)
Diesel	3,142	0.8	48.8	7.075	15.8	2.83	4.07 (g/te fuel)

How to report movement of waste

You must classify wastes using the European Waste Catalogue 6-digit codes and the relevant Waste Framework Directive disposal or recovery codes. Check the ‘reporting codes list’ in the pollution inventory reporting guidance notes.

Worked examples of emission calculations

Example air emissions from filling bulk storage tanks with no abatement equipment in place

If the composition of the waste solvent in the bulk container stays reasonably constant throughout the year, you can do this calculation using the annual tonnage of waste solvents received. Alternatively, the emissions from each addition of waste solvent can be calculated and summed for the whole year, as shown here.

Assume that you receive 1,000 kg of predominantly waste benzene. You add this to a waste solvent storage tank containing a two-component mixture of benzene and toluene in a % mole fraction ratio of 95:5.

For the purposes of this equation, vapour pressures have been taken from Perry’s Chemical Engineers Handbook (7th edition, chapter 2).

• VP_benzene = 12.46 kPa at 25°C
• VP_toluene = 4.97 kPa at 25°C

Therefore, using Equation 1, mole fractions in displaced vapour are:

y_benzene = x_benzene x VP_benzene / P

• = 0.95 x 12.46 kPa / 101.3 kPa
• = 0.117

y_toluene = x_toluene x VP_toluene / P

• = 0.05 x 4.97 kPa / 101.3 kPa
• = 0.0025

Volume of vapour displaced equals the volume of liquid added.

The 1,000 kg of waste benzene added (density at 25°C = 0.872 kg/l), gives an added volume of 1,000 / 0.872 = 1,147 litres.

Number of moles of saturated vapour released = 1,147 / 24.436 = 46.9.

So, number of moles of toluene = 46.9 x 0.0025 = 0.12, giving a mass of toluene emitted of 0.12 x 92 = 11 g.

Number of moles of benzene = 46.9 x 0.117 = 5.48, giving a mass of benzene emitted of 5.48 x 78 = 427 g.

The sum of all such emissions from each waste solvent addition gives you the annual mass estimate for air emissions from this part of the operation. Ideally, you should make allowance for any changes with time in the composition of the stored bulk waste solvent mixture.

Example pollution inventory declaration from a waste transfer station

Assumptions

This is a hazardous waste transfer station with an impermeable base. It has bulking areas with blind sumps and a roof. Solvent storage tanks are in a separately bunded area with activated carbon filters on vents. Thermal outbreathing and head space displacement losses due to charging the storage tanks are scrubbed prior to atmospheric discharge.

Loading, unloading, and drum storage areas of the site are in the open and drain to interceptor, hence to sewer. There is continual monitoring of pH and flowrate, weekly monitoring of chemical oxygen demand (COD), metals, oil, ammoniacal nitrogen, and suspended solids in the sewer discharge.

Packing materials and old contaminated containers are sent to landfill.

The site handles a very wide range of materials, but there are 6 major solvent streams (all percentages are by mass):

• halogenated solvents comprise an average
  • 60% methylene chloride (dichloromethane)
  • 10% trichloroethylene
  • 10% methyl chloroform (1,1,1-trichloroethane)
  • 20% solids (that is, 80% solvents in total)
• non-halogenated solvents comprise an average:
  • 30% xylenes
  • 10% toluene
  • 10% acetone
  • 20% others (mainly MEK, ethanol, acetaldehyde (ethanal), methanol and aliphatic C10-C12 hydrocarbons)
  • 30% solids and water (that is, 70% solvents in total)

The other major waste streams are:

• dilute hydrochloric acid and zinc
• sulfuric acid and phosphoric acid from metal processing
• soluble oils
• dilute caustic soda
• dilute ammonia solutions from photographic processes
• aqueous paint residues
• aqueous adhesive residues
• ethylene glycol

All of these are bulked prior to onward transfer or storage.

Emission scoping operation 1: repacking and labelling laboratory chemicals

Potential emissions: None

No incidences of damage to containers noted in site diary.

Emission scoping operation 2: decanting into IBCs

Potential emissions - 5 streams handled:

• halogenated solvents
• non-halogenated cemfuel
• aqueous organic
• caustic, dilute acids
• drums shredded prior to recycling or landfill

The key streams are:

• cemfuel (120 te produced per year and then stored at the site for tankering - see Operation 3 below)
• halogenated materials (60 te produced per year) that leave the site in IBCs

Emissions are due to the venting of residues in the emptied containers after bulking. Using equations described in the guidance, this is about 1% of the solvent output.

Total atmospheric emissions are therefore:

• 0.01 x 60 x 0.8 te = 480 kg halogenated solvents (80% of the solvent waste is solvent)
• 0.01 x 120 x 0.7 te = 840 kg non-halogenated solvents (70% of the solvent waste is solvent)

This gives an initial assessment of the VOC emissions. These are then broken down into species.

Halogenated solvents: total 480 kg:

• 60% methylene chloride; 0.6 x 0.01 x 60 te = 360 kg
• 10% trichloroethylene; 0.1 x 0.01 x 60 te = 60 kg
• 10% methyl chloroform; 0.1 x 0.01 x 60 te = 60 kg

Non-halogenated solvents: total 840 kg:

• 30% xylenes; 0.3 x 0.01 x 120 te = 360 kg
• 10% toluene; 0.1 x 0.01 x 120 te = 120 kg
• emissions of acetone, acetaldehyde, ethanol, methanol, MEK, and aliphatic hydrocarbons to air are not reportable except as part of the total NMVOC emission

Total NMVOC emissions are 1,320 kg (that is, 480kg + 840kg).

Emission scoping operation 3: charging storage tanks

Potential emissions: the tanks are connected to scrubber units to control outbreathing due to thermal change or tank filling. There is a balancing system in place for filling tankers. There will be discharges of all solvent mixtures in store, but these will be small. IBCs are emptied using a pump. Residual volatile liquids discharge to atmosphere.

The calculations of emissions are the same as Operation 2, but the discharge is only 0.5% of output.

The tanks handle 120 te of waste from the IBCs filled at the site and a further 260 te of waste that arrives at the site in IBCs.

Total emissions:

• 30% xylenes; 380 x 0.3 x 0.005 te = 570 kg
• 10% toluene; 380 x 0.1 x 0.005 te = 190 kg
• total NMVOC emissions are 380 x 0.7 x 0.005 te = 1,330 kg

Monitored emissions from the site: to sewer

Potential emissions: monitoring for COD, metals, oil, ammoniacal nitrogen, suspended solids and flowrate.

Weekly samples are taken, but these are not proportional to flow volumes. Example results are given as Table 2: these are 52 spot samples, which are not necessarily representative of throughput. Nearly all results show low values and sometimes below the level of determination. There is one comparatively high ammoniacal nitrogen reading, but no obvious correlation with any incident on the site.

For an estimated weekly load: multiply weekly results by weekly flowrate and sum to give annual emissions to sewer.

Table 2: Example sampling results for three weeks of sewage emissions testing, with example annual totals

Week No.	Flow (m3)	COD (mg/l)	COD discharged (g)	TOC = COD/3 (g)	NH3-N (mg/l)	NH3-N discharged (g)
1	2.1	190	399	133	<0.1	0.1
2	1.6	460	736	245	0.3	0.48
3	0.2	610	122	41	1.9	0.38
Annual total	n/a	n/a	n/a	5,980	n/a	14

Other relevant species (from the main list of wastes at the plant) are xylene, toluene, chloride and phosphorus. These are declared as emissions below reporting threshold (brt), but actual values could be given if available.

In summary, the total emissions from operations undertaken at this example site are:

• repacking and labelling of laboratory chemicals:
  • no emissions to air or sewer
• decanting into IBCs:
  • 60 kg methyl chloroform to air
  • 360 kg methylene chloride to air
  • 120 kg toluene to air
  • 60 kg trichlorethylene to air
  • 360 kg xylenes to air
  • 1320 kg NMVOCs to air
  • several species likely to be below reporting threshold to sewer - solvent species metals, total chloride, total nitrogen, total phosphorus, TOC
• transfer from IBCs to solvent storage tanks:
  • 190 kg toluene to air
  • 570 kg xylenes to air
  • 1330 kg NMVOCs to air
  • xylenes and TOC to sewer (not quantified here)

You should report the total value from all processes combined. If the result is below the reporting threshold, you can either give the actual value or write ‘brt’. Where possible, we encourage you to provide actual values.

Any substances which are not released from your site, you should record as ‘n/a’.