FAQ's - Odour

1. What are the likely sources of odour at a landfill?

Odour sources from a landfill include leachate and landfill gas created from the decomposition of the waste, as well as newly deposited materials on top of the waste mass, and delivery vehicles carrying waste to the site.

Typical measures to minimise odour at landfills include the following:

  1. Capturing landfill gas and combusting it using a landfill gas engine or flare;
  2. Keeping the tipping area as small as possible;
  3. Covering waste as soon as possible;
  4. Installing capping over the waste when operational areas have been completed;
  5. Ensuring the landfill gas management system is operating effectively and installed once gas is being produced;
  6. Keeping leachate levels low; and
  7. Avoiding over-tipping older areas of waste.

Our officers ensure the operator correctly identifies the source of the odour and that the subsequent action plan is appropriate and focused. However, even if an action plan is completed as expected, sometimes a residual odour may persist.

2. How do you regulate off-site odour from the landfill?

The permit includes a condition that requires the operator to prevent odour off site or, where that is not possible, to keep it to a minimum. The operator will describe how it will achieve this in a document called an Odour Management Plan (OMP). The OMP must be kept up to date and each revision is assessed by our officers to ensure it covers all the key areas of operations in relation to odour management.

Officers assess compliance with the odour condition by:

  1. Verifying the presence, type and intensity of odour in the vicinity of a permitted site,
  2. Identifying whether the site is the likely source of the odour, and if so going on site to determine the causes of any odours and whether the operator is taking appropriate measures to control the odour.

Officers carry out odour investigations (including off-site odour assessments) in accordance with our guidance and by reference to published odour management guidance.

Odour intensity describes the strength of the odour as perceived by an individual officer. We record odour intensity using a scale of 0 to 6, where 0 = no odour, 3 = distinct odour and 6 = extremely strong odour.

A permit breach will only be recorded where:

  1. Odour due to activities on the site at a level likely to cause pollution outside the site boundary is substantiated by an officer, and
  2. The operator is not taking all appropriate measures to control that odour.

If the operator is taking appropriate measures then no breach of the permit has occurred, even if there is some odour. We would expect the operator to identify appropriate measures in its OMP, but we may require additional measures if serious odour pollution occurs.

The operator is informed about any odour reports we receive that relate to the site, but we do not release personal data, so they cannot identify individual reporters. The operator is expected to respond to reports of odour in accordance with its Odour Management Plan (OMP) for the site, and to advise us of any resulting changes to operations.

Non-compliance with the odour condition is scored on the basis of actual impact, applying the Environment Agency’s Compliance Classification Scheme (CCS) guidance: https://www.gov.uk/government/publications/assessing-and-scoring-environmental-permit-compliance.

Where necessary, we consider further regulatory action in accordance with Defra guidance on the Environmental Permitting (England and Wales) Regulations 2016 (EPR) (the Core Guidance), the Regulators’ Code, and our own enforcement and sanctions policy.

We describe the action we have taken and the measures we have required the operator to implement in our Plan to reduce hydrogen sulphide emissions, with the 3 key objectives to contain, capture and destroy the landfill gas.

3. What measures are in place to minimise the odour at a landfill site?

Typical measures to minimise odour at landfills include the following:

  • Capturing landfill gas and combusting it using a landfill gas engine or flare;
  • Keeping the tipping area as small as possible;
  • Covering waste as soon as possible;
  • Installing capping over the waste when operational areas have been completed
  • Ensuring the landfill gas management system is operating effectively and installed once gas is being produced;
  • Keeping leachate levels low; and
  • Avoiding over-tipping older areas of waste.

This is not an exhaustive list, there are other measures which can be used on a site-by-site basis.

4. Why do you use ‘sniff tests’ and not monitoring equipment for odour assessments?

Sniff testing is the name given to the assessment of smells using the human nose. Some people are surprised that the human nose is used rather than monitoring equipment. There are several reasons for this.

The odour condition in environmental permits require odour pollution to be “perceived by an authorised officer” which means that it is necessary for an officer to actually smell the odour themselves.

Odour intensity describes the strength of the odour as perceived by an individual officer. Our officers record odour intensity using a scale of 0 to 6 as follows:

  1. No odour
  2. Very faint odour (need to inhale into the wind to smell anything)
  3. Faint odour (you can detect an odour when you inhale normally)
  4. Distinct odour (there is clearly an odour in the air as you leave your car or enter the area)
  5. Strong odour (a bearable odour but strong, you could stay in the area for some time)
  6. Very strong odour (unpleasantly strong, you will want to leave the area quickly)
  7. Extremely strong odour (likely to cause nausea and a strong need to remove yourself from the odour immediately).

The human nose is still the best means we have for detecting the full range of gases that cause odour. The concentrations at which these odorous gases are present in outdoor (ambient) air is usually very low beyond site boundaries (even if the smell is intense), and few pieces of equipment are sensitive enough to pick up the full range of these gases, when compared to the nose. In addition, sniff testing is physically versatile and allows us to assess odour at most locations without restrictions relating to external power, weather conditions, terrain etc.

5. What factors can impact the odour at a landfill site?

Factors such as improvement works being carried out on site and changes in the weather can impact odour levels. Concentrations of landfill gas emissions generally increase during periods of colder weather and still wind conditions. With less ability for the landfill gas emissions to disperse, there is a greater potential for these emissions to cause an odour nuisance in the local area. By contrast, during periods of warmer weather, the gases are naturally more diluted due to higher temperatures and rising air. This means improvements from measures implemented at Walleys Quarry Landfill to reduce odour could be less noticeable in the winter and spring. We have created an animation on How weather affects landfill sites.

6. What is the ‘perfume’ we can sometimes smell outside the site?

The “perfumes” are called deodorisers. They are an industrial vapour-based system using non-toxic, food biodegradable product mixed with mains water, which is widely used for odour control around site perimeters. We have confirmed that WQLS is using ‘Odr’, a proprietary industrial odour neutraliser. The odour neutraliser that has been used along the line parallel to Cemetery Road is the ‘Cotton Fresh’ fragrance whereas for the north-eastern boundary line the ‘Cherry’ fragrance has been used.

When we first started to receive complaints about the deodoriser mists, WQLS was using its deodoriser so that it covered the area closer to the site entrance. Since we shared these reports, it has been re-positioned and WQLS has reduced the system pressure. When officers carry out off-site odour assessments before they inspect the site, they have smelt a ‘fresh washing’ odour outside the site perimeter, but have not considered it to cause offence to human senses.

We do not consider the use of deodorisers to be an appropriate measure for controlling odour when used as a sole odour control method, but it is a technique that an operator can choose to use as part of its Odour Management Plan. If the use of a deodoriser presents a hazard to road users, then Staffordshire County Council as highway authority and/or the police, should be notified.

1. What are the likely sources of odour at a landfill?

Odour sources from a landfill include leachate and landfill gas created from the decomposition of the waste, as well as newly deposited materials on top of the waste mass, and delivery vehicles carrying waste to the site.

Typical measures to minimise odour at landfills include the following:

  1. Capturing landfill gas and combusting it using a landfill gas engine or flare;
  2. Keeping the tipping area as small as possible;
  3. Covering waste as soon as possible;
  4. Installing capping over the waste when operational areas have been completed;
  5. Ensuring the landfill gas management system is operating effectively and installed once gas is being produced;
  6. Keeping leachate levels low; and
  7. Avoiding over-tipping older areas of waste.

Our officers ensure the operator correctly identifies the source of the odour and that the subsequent action plan is appropriate and focused. However, even if an action plan is completed as expected, sometimes a residual odour may persist.

2. How do you regulate off-site odour from the landfill?

The permit includes a condition that requires the operator to prevent odour off site or, where that is not possible, to keep it to a minimum. The operator will describe how it will achieve this in a document called an Odour Management Plan (OMP). The OMP must be kept up to date and each revision is assessed by our officers to ensure it covers all the key areas of operations in relation to odour management.

Officers assess compliance with the odour condition by:

  1. Verifying the presence, type and intensity of odour in the vicinity of a permitted site,
  2. Identifying whether the site is the likely source of the odour, and if so going on site to determine the causes of any odours and whether the operator is taking appropriate measures to control the odour.

Officers carry out odour investigations (including off-site odour assessments) in accordance with our guidance and by reference to published odour management guidance.

Odour intensity describes the strength of the odour as perceived by an individual officer. We record odour intensity using a scale of 0 to 6, where 0 = no odour, 3 = distinct odour and 6 = extremely strong odour.

A permit breach will only be recorded where:

  1. Odour due to activities on the site at a level likely to cause pollution outside the site boundary is substantiated by an officer, and
  2. The operator is not taking all appropriate measures to control that odour.

If the operator is taking appropriate measures then no breach of the permit has occurred, even if there is some odour. We would expect the operator to identify appropriate measures in its OMP, but we may require additional measures if serious odour pollution occurs.

The operator is informed about any odour reports we receive that relate to the site, but we do not release personal data, so they cannot identify individual reporters. The operator is expected to respond to reports of odour in accordance with its Odour Management Plan (OMP) for the site, and to advise us of any resulting changes to operations.

Non-compliance with the odour condition is scored on the basis of actual impact, applying the Environment Agency’s Compliance Classification Scheme (CCS) guidance: https://www.gov.uk/government/publications/assessing-and-scoring-environmental-permit-compliance.

Where necessary, we consider further regulatory action in accordance with Defra guidance on the Environmental Permitting (England and Wales) Regulations 2016 (EPR) (the Core Guidance), the Regulators’ Code, and our own enforcement and sanctions policy.

We describe the action we have taken and the measures we have required the operator to implement in our Plan to reduce hydrogen sulphide emissions, with the 3 key objectives to contain, capture and destroy the landfill gas.

3. What measures are in place to minimise the odour at a landfill site?

Typical measures to minimise odour at landfills include the following:

  • Capturing landfill gas and combusting it using a landfill gas engine or flare;
  • Keeping the tipping area as small as possible;
  • Covering waste as soon as possible;
  • Installing capping over the waste when operational areas have been completed
  • Ensuring the landfill gas management system is operating effectively and installed once gas is being produced;
  • Keeping leachate levels low; and
  • Avoiding over-tipping older areas of waste.

This is not an exhaustive list, there are other measures which can be used on a site-by-site basis.

4. Why do you use ‘sniff tests’ and not monitoring equipment for odour assessments?

Sniff testing is the name given to the assessment of smells using the human nose. Some people are surprised that the human nose is used rather than monitoring equipment. There are several reasons for this.

The odour condition in environmental permits require odour pollution to be “perceived by an authorised officer” which means that it is necessary for an officer to actually smell the odour themselves.

Odour intensity describes the strength of the odour as perceived by an individual officer. Our officers record odour intensity using a scale of 0 to 6 as follows:

  1. No odour
  2. Very faint odour (need to inhale into the wind to smell anything)
  3. Faint odour (you can detect an odour when you inhale normally)
  4. Distinct odour (there is clearly an odour in the air as you leave your car or enter the area)
  5. Strong odour (a bearable odour but strong, you could stay in the area for some time)
  6. Very strong odour (unpleasantly strong, you will want to leave the area quickly)
  7. Extremely strong odour (likely to cause nausea and a strong need to remove yourself from the odour immediately).

The human nose is still the best means we have for detecting the full range of gases that cause odour. The concentrations at which these odorous gases are present in outdoor (ambient) air is usually very low beyond site boundaries (even if the smell is intense), and few pieces of equipment are sensitive enough to pick up the full range of these gases, when compared to the nose. In addition, sniff testing is physically versatile and allows us to assess odour at most locations without restrictions relating to external power, weather conditions, terrain etc.

5. What factors can impact the odour at a landfill site?

Factors such as improvement works being carried out on site and changes in the weather can impact odour levels. Concentrations of landfill gas emissions generally increase during periods of colder weather and still wind conditions. With less ability for the landfill gas emissions to disperse, there is a greater potential for these emissions to cause an odour nuisance in the local area. By contrast, during periods of warmer weather, the gases are naturally more diluted due to higher temperatures and rising air. This means improvements from measures implemented at Walleys Quarry Landfill to reduce odour could be less noticeable in the winter and spring. We have created an animation on How weather affects landfill sites.

6. What is the ‘perfume’ we can sometimes smell outside the site?

The “perfumes” are called deodorisers. They are an industrial vapour-based system using non-toxic, food biodegradable product mixed with mains water, which is widely used for odour control around site perimeters. We have confirmed that WQLS is using ‘Odr’, a proprietary industrial odour neutraliser. The odour neutraliser that has been used along the line parallel to Cemetery Road is the ‘Cotton Fresh’ fragrance whereas for the north-eastern boundary line the ‘Cherry’ fragrance has been used.

When we first started to receive complaints about the deodoriser mists, WQLS was using its deodoriser so that it covered the area closer to the site entrance. Since we shared these reports, it has been re-positioned and WQLS has reduced the system pressure. When officers carry out off-site odour assessments before they inspect the site, they have smelt a ‘fresh washing’ odour outside the site perimeter, but have not considered it to cause offence to human senses.

We do not consider the use of deodorisers to be an appropriate measure for controlling odour when used as a sole odour control method, but it is a technique that an operator can choose to use as part of its Odour Management Plan. If the use of a deodoriser presents a hazard to road users, then Staffordshire County Council as highway authority and/or the police, should be notified.

Page published: 08 Mar 2023, 12:09 PM