Following on from yesterday’s air quality monitoring update, we would like to provide an update on this week’s progress at the Lower Compton Landfill and the actions being taken to address odour concerns affecting communities in Calne and the surrounding area.

This week, the Environment Agency visited Lower Compton Landfill to review site operations and progress against the action plan required by the Environment Agency. We can confirm that all permanent and temporary capping works have now been completed ahead of schedule. Hills has also confirmed that additional landfill gas wells will be installed from 13 July to increase gas capture and further reduce emissions from the site. The site operator has shared an update on the works here: https://www.hills-waste.co.uk/news/northacre-mbt-lower-compton-landfill-and-ukhsa-report

As outlined in our update yesterday on the publication of the UK Health Security Agency (UKHSA) Public Health Risk Assessment, monitoring data collected by the Environment Agency supports findings from our inspections and off-site odour assessments. The ambient air monitoring station remains in place and will help us to establish whether the work currently being completed by Hills is minimising landfill gas odour. We will carry out our assessment in August, once the installation of the permanent gas infrastructure has been completed.

As previously communicated, waste that would normally be processed at the Northacre Mechanical Biological Treatment (MBT) facility in Westbury continues to be redirected to Lower Compton while maintenance works are completed there. We have emphasised to Hills the importance of managing this waste appropriately and minimising any impact on local communities. Hills has confirmed that all additional waste diverted from Northacre MBT is being landfilled immediately to reduce any potential impact. Hills have shared that they expect the MBT plant will restart from Monday 20 July.

The Environment Agency will continue to regulate the site closely and carry out inspections and off-site odour assessments to monitor the effectiveness of the measures implemented. We will continue to work with Hills Waste Solutions, Wiltshire Council and UKHSA to ensure appropriate action is taken where necessary.

As previously announced, a multi-agency community drop-in event will take place on 21 July 2026, from 4pm to 7pm at Calne Town Hall, where residents can discuss the recent air quality assessment and ongoing work at the site with representatives from the Environment Agency, UKHSA, Wiltshire Council and Hills Waste Solutions.

Environment Agency staff monitoring at the Lower Compton site Jul 26

The UK Health Security Agency (UKHSA) has now completed and published a public health risk assessment using data collected by the Environment Agency's Mobile Monitoring Facility (MMF) in the Calne community, located at Priestley Primary School.

The MMF provides continuous air quality monitoring, including measurements of hydrogen sulphide, methane and particulate matter concentrations. We recognise the community's desire for transparency and openness; therefore, the full ratified dataset used to inform the assessment is available on our website.

The full UKHSA report, together with an executive summary, can be accessed here:

UKHSA PHRA Summary

UKHSA PHRA Full Report

We have also provided the Environment Agency Study of Ambient Air Quality at Lower Compton:

Environment Agency Air Quality Study

MMF Air Quality Dataset (Excel)

We, Wiltshire Council and UKHSA have also prepared a Questions and Answers (Q&A) to help explain the findings and address some of the questions residents may have when reading the report.

The ambient air monitoring data produced by the Environment Agency, and analysed in this report, shows that there is a source of hydrogen sulphide and methane in the direction of the Lower Compton Landfill Site. 

This confirms the findings of our inspections and off-site odour assessments, and supports the Environment Agency’s regulatory decisions, including requiring Hills to bring capping works forward and change the ways they manage odour.

Community Drop-in Event 21 July 2026

We are hosting a multi-agency drop-in event where residents can discuss the report's findings directly with representatives from the agencies involved in responding to the odour issues in Calne.

Calne Landfill Odour Response Drop-in Event

Date: 21 July 2026
Time: 4:00pm – 7:00pm
Location: Large Hall, Calne Town Hall, SN11 0EN

Representatives from multiple agencies will be available to answer questions and provide information:

• Environment Agency - Air quality monitoring, monitoring methodology and site regulation. Contact: wessexenquiries@environment-agency.gov.uk
• UKHSA - Technical findings of the UKHSA assessment and further information on UKHSA advice. Contact: enquiries@ukhsa.gov.uk
• Wiltshire Council – Environmental Health Team and statutory nuisance investigations. For more information: www.wiltshire.gov.uk/article/1833/Smells-and-odours
• Health concerns, medical advice and Public Health issues – Wiltshire Council and UKHSA advise if you have any concerns about your health, please contact your GP or NHS 111 for individual medical advice in the first instance. If you have any further public health-related queries, you can email Wiltshire Council Public Health at publichealth@wiltshire.gov.uk, who can help direct your query to the most appropriate organisation for a response.
• Hills Waste Solutions – Site operations. Contact: www.hills-group.co.uk/contact-us/

About the Monitoring Programme

The monitoring location at Priestley Primary School was carefully selected using a range of factors, including prevailing wind patterns, the predicted movement of landfill emissions and the geographical distribution of odour reports received from the community.

In addition to measuring air quality, the Mobile Monitoring Facility collected meteorological information such as wind speed, wind direction, temperature and atmospheric pressure. This data helps us understand when emissions may have occurred and whether they could be linked to landfill operations.

The monitoring programme supported our extensive field observations from Environment Agency officers who responded to odour reports across the community. Together, these sources of information have provided a comprehensive evidence base to support our ongoing regulatory work.

You can read more about the monitoring programme in our Questions and Answers.

Environment Agency regulation

The Environment Agency is responsible for regulating the landfill site and ensuring compliance with the conditions of its environmental permit.

As the environmental regulator, we have taken extensive action to require Hills Waste Solutions to address the source of the odour affecting the Calne community. These improvement works are now nearing completion.

We will continue to regulate the site closely and will take further enforcement action where necessary to ensure permit compliance and minimise environmental impacts.

Responsibility for investigating odour nuisance sits with Wiltshire Council. Public health matters are the responsibility of the UKHSA and Wiltshire Council through their director of public health. We will continue to work closely with both organisations.

Following on from our previous briefings, we would like to provide a further update on the odour concerns being experienced in Calne and Westbury.

Following the failure of the cranes at the Westbury Mechanical Biological Treatment (MBT) facility, Hills has taken the decision to temporarily stop accepting new household waste at the site. You can read more about Hills’ decision in their update here: https://www.hills-waste.co.uk/news/update-on-northacre-mbt-and-lower-compton-landfill

As a result, Hills has implemented its contingency plan, which has been agreed with Wiltshire Council, by redirecting household waste collections that would normally be processed at Westbury to the Hills facility at Compton Bassett, near Calne. This will enable collections to continue while Hills addresses the issue at the Westbury site.

We recognise that this change may increase concerns about odour in both communities, particularly with further periods of hot weather forecast. In Westbury, there may be increased odour associated with doors being opened to carry out the necessary repair work. We have inspected the transfer station in Compton Bassett today, ensuring that Hills are using appropriate measures to minimise odour from the additional waste being delivered.

We fully appreciate that this situation is far from ideal for residents. We are working closely and urgently with Hills and Wiltshire Council to identify and implement measures that will minimise the impact of the additional waste being processed at Compton Bassett and to reduce odour wherever possible.

Please be assured that officers will continue to monitor odour levels in Westbury throughout the weekend and will respond to reports from residents across the area as they are received. We understand how challenging waste-related odours can be, especially during periods of warm weather, and we remain committed to investigating concerns and taking appropriate action where necessary.

We are also continuing to work with Wiltshire Council and the UKHSA to arrange community engagement events in both Calne and Westbury. These sessions will provide residents with an opportunity to speak directly with representatives from the relevant organisations, ask questions, and share their experiences. Details of dates and venues will be shared as soon as arrangements are confirmed.

Progress continues with the capping works at the Lower Compton landfill site

We understand that many people in the community are feeling frustrated and upset about odour, particularly over the past week. Over 100 reports were received across the weekend, and we recognise the real impact this is having on day-to-day life, especially during the current hot weather.

Periods of heat can make odours more noticeable and allow them to travel further. While this helps explain the recent increase, we know this does not lessen the experience for those affected, and we want to reassure residents that concerns are being taken seriously.

Our officers have been actively responding to reports across the area. During these visits, odour levels have generally been assessed as faint to transient. However, we fully appreciate that even intermittent odours can be unpleasant, disruptive, and, at times, distressing.

As the regulator, we are continuing to robustly oversee the permanent capping works that we have required Hills to deliver in order to bring the site back into full compliance with its environmental permit. These works are a regulatory requirement and are expected to be completed by the end of July.

Following completion, we will work in partnership with Wiltshire Council Environmental Health Officers to monitor odour levels in the community and assess the effectiveness of the capping. We will take further regulatory action if necessary to ensure the site is operating in compliance and impacts on the community are appropriately controlled.

Environment Agency staff monitoring at the Lower Compton site

Upcoming engagement

We are working with our partners at Wiltshire Council and the UK Health Security Agency (UKHSA) to arrange a community engagement event in Calne. This will provide residents with an opportunity to speak directly with us and partners, ask questions, and raise any concerns about the ongoing odour issues.

We are committed to ensuring the community has access to clear information and the opportunity to be heard. Details of the event, including date and venue, will be shared as soon as they are confirmed.

Public Health Advice

UK Health Security Agency (UKHSA) provides specialist public health advice to the Wiltshire Council and partners, including the Environment Agency, to protect the public’s health. UKHSA has no regulatory or intervention powers in this area.

Lucy McCann, Consultant in Health Protection at UKHSA South West, said: “Everyone reacts to odours differently, and some people are more sensitive to environmental odours than others.

Landfill gas contains hydrogen sulphide, which even in very small quantities produces a strong smell similar to rotten eggs and may be noticeable to nearby residents.

At the levels currently being detected around this site, the risk to health is likely to be low. The Environment Agency continues to monitor levels on-site and in the wider community.

Even when levels are low, strong smells can still be unpleasant and may affect wellbeing. Some people may experience symptoms such as headaches, nausea, or dizziness, particularly if exposed for longer periods.”

Advice for Residents

UKHSA advises residents to:

• Close windows in the evening if outdoor odours are noticeable, and reopen them in the morning when conditions improve
• Use weather forecasts to identify times your property is downwind (when closing windows can reduce landfill odour indoors) and upwind (when opening windows can reduce any residual odour indoors)
• Report odour to the Environment Agency

For further information on UKHSA advice and guidance please contact: Enquiries@ukhsa.gov.uk

If you have any concerns about your health, please contact your GP or NHS 111 for individual medical advice.

If you have any further public health-related queries, you can email Wiltshire Council Public Health at publichealth@wiltshire.gov.uk, who can help direct your query to the most appropriate organisation for a response.

Odour Update 19 June 2026: Northacre MBT Facility; Westbury

In our previous update, we reported that Hills had an issue with their biofilter and that they had carried out maintenance work which was expected to help reduce odour levels. However, Hills have now confirmed that the new biofilter is currently not operating effectively due to a further fault with the newly installed moisture control sensor. This has resulted in the system becoming too wet and not functioning as designed.

While a back-up system enabled the issue to be identified quickly, we recognise that any increase is concerning and understand the frustration this causes within the community. We have required Hills to take action to rectify this as quickly as possible.

We have independently observed an increase in odour this week, which we attribute to these ongoing biofilter failures. The odour our officers are detecting is primarily that associated with general household waste and not hydrogen sulphide that is present at other waste sites.

Following our investigation and direct engagement with Hills, we have formally identified that the site is currently not compliant with the conditions of its environmental permit. We have made clear to the operator that this situation is unacceptable and have required immediate corrective action.

As a result, we are considering enforcement action and have instructed Hills to resolve the issues with the biofilter as a matter of urgency. Our priority is to ensure the operator meets its legal obligations and that the impact on the community is minimised.

Our officers have been proactively monitoring conditions on site and are continuing to respond promptly to odour reports. This increased level of oversight will continue until we are satisfied that the issues have been fully resolved and that control measures are working reliably.

We want to reassure residents that we are holding the operator to account and taking firm regulatory action to resolve the situation. Your reports play a vital role in supporting this work, and we encourage you to continue reporting any odour incidents.

We appreciate the community’s continued patience and will provide further updates as soon as there is meaningful progress.

Environment Agency staff monitoring odour in Westbury

Odour Update 22 June 2026: Lower Compton Landfill Site, Calne

Over the weekend, we received over 100 reports of odour. We have had staff out proactively monitoring throughout the weekend to corroborate reports.

We continue to ensure that Hills carries out improvement works to the Lower Compton landfill site to the standard we expect. Good progress has been made with the capping works, with the subsoil restoration layer now spread over approximately 60% of the permanent capping to protect the clay. Once the works are complete, we expect odour levels to improve, and we will carry out extra odour monitoring to assess the change in levels.

On modern landfills, engineering work is carried out under a Construction Quality Assurance (CQA) plan, which has to be accepted by the Environment Agency prior to work being started. Information about CQA for landfills can be found here: Landfill operators: environmental permits - Construction quality assurance (CQA) - Guidance - GOV.UK

Inspections of the construction work include:

• Assessment of field testing and lab sample results to confirm the clay used is within specification.
• Site walkovers to check for any non-conforming material (such as large rocks) and to confirm the works are being carried out as per the approved CQA plan.
• Reviewing the CQA Inspectors records and ensuring the work has the required level of supervision.

Where work has not met the required standard, or where fugitive emissions have been identified, we have required the contractor to rectify and repeat the work.

Residents may be aware that earlier this week there was a fire at a neighbouring recycling centre. This was unrelated to the permanent capping works at Lower Compton Landfill and has not affected or delayed the remedial works.

Environment Agency staff monitoring at the Lower Compton siteMonitoring

In recent weeks, we have shared information on how we are monitoring odour and air quality (see: https://engageenvironmentagency.uk.engagementhq.com/wessex-regulated-industry-sites/news_feed/odour-response-in-calne).

We have a monitoring facility at Priestley Primary School. A range of factors were considered when selecting the monitoring location. The monitoring facility has been positioned to reflect:

• The likely route that hydrogen sulphide would travel into the town; odours can move along valleys at night due to cooler, denser air
• Residential areas where high numbers of odour reports have been received on the eastern side of Calne, ensuring monitoring reflects areas of highest concern
• The prevailing wind direction, local topography, and the need for suitable hard standing and a mains power supply

The Mobile Monitoring Facility (MMF) measures ambient air quality in the area, which may include emissions from multiple local sources. As well as methane and hydrogen sulphide levels, we also record meteorological conditions, including wind direction, wind speed, temperature, and atmospheric pressure.

The data collected from the MMF has now been sent to the UKHSA to allow them to make an independent health impact assessment.

Annotated photograph of an MMF exterior

Odour Update 12 June 2026: Lower Compton Landfill Site, Calne

We recognise the ongoing impact that odour is having on residents, and we are continuing to prioritise work to address these concerns as quickly as possible.

This week we have been out on site again to ensure Hills are delivering the actions that we have required of them to bring the site back into compliance with its environmental permit. This includes the accelerated permanent capping works.

Permanent capping works progressing at the Lower Compton Hills site, June 2026Environment Agency and Wiltshire Council staff on site at Lower Compton Landfill, June 2026

We have also been out on site with the Wiltshire Council Environmental Health team who are monitoring odour for statutory nuisance and public health. By sharing data and working together we are ensuring that the odour is being investigated. While we work side by side, we have distinct roles:

• The Environment Agency assesses off-site odour to ensure compliance with environmental permit conditions
• Wiltshire Council assesses statutory nuisance impacts. You can find out more about Wiltshire Council’s role in monitoring for odour here: www.wiltshire.gov.uk/env-health-pollution

How we monitor

Our regulatory team assesses compliance in several ways, including site inspections, audits, off-site odour assessments, and reviewing operator reports and monitoring data.

We carry out monitoring in the community to substantiate odour reports and assess whether odour is occurring off-site, as required by the permit. Our presence in the community is focused on identifying and evidencing off-site odour so action can be taken where required.

The main way we assess compliance is through “sniff testing”, using trained officers to detect and assess odours. This is required by permit conditions and remains the most effective method, as the human nose can detect the full range of gases responsible for odour at very low levels. It is important to be clear that this type of monitoring is for regulatory compliance purposes and not to directly assess health impacts.

We also use a Mobile Monitoring Facility (MMF) to measure ambient air quality. This supports our assessment from sniff testing. The MMFs monitor for methane, hydrogen sulphide, and particulates.

We understand that residents have concerns about potential health effects, and we take these concerns seriously. While our role is to assess compliance with environmental permit conditions, particularly whether odour is affecting areas beyond the site, the data we collect is shared with the UK Health Security Agency (UKHSA).

UKHSA are the independent public health experts responsible for assessing any potential impacts on health. They review the monitoring data and determine whether there are any risks to the community.

It is important to recognise that odour and health impacts are assessed in different ways. Odour can be strong and disruptive at levels that are still very low in terms of measurable gas concentrations, meaning something can be clearly noticeable and unpleasant without necessarily being harmful to health.

Our approach reflects this. We use sniff testing to assess odour impact and compliance with permit conditions, and we use monitoring data to support this and to inform UKHSA’s independent health assessment

Our aim is to ensure that odour is reduced to a level where it is no longer causing unacceptable impact beyond the site boundary. The actions being taken, particularly capping and improved gas control, are expected to reduce odour, although this may take time to fully resolve. Once the capping works are complete, we will carry out additional odour monitoring to assess how conditions have improved.

We recognise that people want access to monitoring data. This will be published once UKHSA has completed its independent public health assessment, and we will continue to keep the community informed as work progresses.

Odour Update: Northacre MBT Facility; Westbury

We have been receiving an increase in odour reports over the last couple of weeks from some residents in Westbury, and we recognise the impact this can have on daily life and activities. Ensuring that local communities are protected from environmental impacts is a key priority for the Environment Agency.

We regulate the Northacre MBT facility and, following both community feedback and our own monitoring, we acted quickly to engage with the site operator to understand what was causing the increase in odour and to ensure action was taken.

What has happened and what is being done

We are aware that some residents have recently experienced stronger or more persistent odours linked to the facility. Whilst our monitoring has suggested that these have generally remained low-level and short-lived, we appreciate that an increase in odour levels is unacceptable.

The operator’s investigation identified a fault within the site’s biofilter system, which is used to control odours. With support from an independent specialist, it was confirmed that a sensor fault caused the system to become too wet. This reduced its ability to treat odorous air effectively.

To address this, the operator has:

• Replaced the faulty sensor
• Installed a backup system to help prevent this happening again
• Regenerated the biofilter this week to restore performance

These actions are expected to improve airflow and reduce odour over the next few days.

Environment Agency staff monitoring for odour in Westbury

We continue to visit the site regularly to ensure measures are being taken to minimise off-site odour and we are maintaining increased odour monitoring to make sure that odour levels return to an acceptable level as soon as possible. If needed, we will take further action to ensure the site operates in line with its permit conditions.

We continue to work with our partners, including Wiltshire Council and we will continue enhanced odour monitoring in the area and remain focused on reducing odour levels. We are committed to keeping residents updated and ensuring residents' concerns are heard and acted on. Please keep up to date with the latest information by checking back on this website and following our social media channels Environment Agency - South and South West | Bristol | Facebook and Environment AgencySW (@EnvAgencySW) / X

What have we done so far?

We understand how unpleasant and frustrating odour can be, especially when it affects your home and day-to-day life. Addressing these concerns is a priority for us.

The Environment Agency regulates waste sites through strict permits, which set out how sites must operate. At the Lower Compton landfill site, our focus has been on making sure the operator Hills meets these requirements, particularly when it comes to reducing odour beyond the site boundary.

In response to the concerns raised by the community, we have had staff actively monitoring odour in the local area since March 2025. This work sits alongside our Ambient Air Monitoring Station, which is based locally and records odour levels around the clock, 24 hours a day.

We are also working closely with our partners:

• Wiltshire Council, which leads on statutory nuisance odour.
• UK Health Security Agency (UKHSA), which provides expert advice on any potential health impacts

Together, we are taking action to ensure that Hills improves its operations and reduces odour as quickly as possible.Environment Agency staff monitoring at the Lower Compton site

What we’ve required the site to do:

• After seeing an increase in odour reports, in March 2026 we required Hills to produce an action plan, this included bringing forward the permanent capping of the current operational area, after we established this was the main source of odour from the landfill site. This is the best long-term solution to minimise odour from a landfill.
• These works are due to be completed by the end of July. We are regularly visiting the site to check that the work is progressing properly and on time.
• We have also required Hills to produce a clear plan setting out how they will minimise odour going forward. This includes addressing changes to waste composition, management procedures on site, and sizing of future landfill cells to allow more frequent capping. We are currently reviewing this plan to make sure it is strong enough and will make a real difference.
• Once the capping works are complete, we will carry out extra odour monitoring to assess the change in odour levels.

Environment Agency staff inspecting the progress of permanent capping works at the Lower Compton Hills waste site, June 2026

What's happening with the data?

We know many residents want clear answers about odour levels and any potential impacts.

We have an air monitoring station in Calne that continuously measures levels of Hydrogen Sulphide, Methane and Particulates. Our specialist monitoring team is currently checking and validating an interim dataset collected between October 2025 and April 2026 to make sure it is accurate and reliable. This is an important step when dealing with detailed scientific information. Once complete, we will share this with the UKHSA who will make public health risk assessment.

Once this process is complete:

• UKHSA will carry out an independent public health risk assessment
• This will help explain whether the odour levels could impact health or be considered a nuisance

We appreciate that waiting for this information can be difficult. While we cannot share the data just yet, we want to reassure you that it will be made public once UKHSA have made their public risk assessment.

When the UKHSA public health risk assessment is complete, we, along with our partner organisations, will hold a community event. This will give you the opportunity to:

• Hear directly from the agencies involved
• Understand what the data shows
• Ask questions and raise concerns
• Learn what further actions are being taken

We are committed to keeping you informed and will share further updates as soon as more information becomes available. In the meantime, your reports remain vital in helping us understand when and where odour is being experienced, and we encourage you to continue reporting any issues.

Permanent capping works progressing at the Lower Compton Hills site, June 2026

Environment Agency staff monitoring at the Lower Compton site