Calne monitoring update 24 September 2026

Between 3 and 26 August the Environment Agency carried out daily odour monitoring to understand whether the engineering work completed in July has been effective.

Through the first three weeks of August, we continued to see high numbers of reports, and officers found landfill gas odour in residential areas. Although this was rated as very faint to faint intensity it was offensive and pervasive in calm, cool conditions.

Assessment of site monitoring data over the same period has identified periods of low/no suction pressure at the gas engine compound, and corresponding downtime. The cause has been identified as filter blockages in the gas lines. Infinis, the company responsible for the gas engines and maintenance of the gas field, are working to establish the root cause. After this issue was identified, preventative maintenance checks were increased, and normal operation was re-established on 21 August.

We believe the supply interruptions are likely to have increased fugitive emissions from Lower Compton landfill, so we extended our enhanced monitoring period to account for this. Odour reports have since reduced and have stayed low through September (14 reports received to date). In part, this will be due to the change in wind direction; we will carry out monitoring in less favourable conditions to assess the effectiveness of the controls on site.

We continue to monitor progress on site. Our surveys have found the recent permanent capping work is effectively minimising emissions from the western half off cell 26D. Point source emissions have been noted around temporary infrastructure in the eastern half of the cell; although this is to be expected, we are requiring Hills to review their monitoring and remediation methods to ensure these are minimised.

Our Air Quality monitoring team have now produced a second report using data gathered up to 6 August by our mobile monitoring facility in Calne. The full report and summary depending on how you view this update can be found by scrolling down ( if accessing from a mobile device) or to the right if viewing via website. The two documents are entitled : UKSA Lower Compton Landfill PHRA Summary and UKHSA Full PHRA for Lower Compton Landfill.

The latest UKHSA risk assessment concludes there are no exceedances of relevant health guidance values. Although peak concentrations of hydrogen sulphide have reduced since March 2026, the data shows periods where the concentration is above the WHO guideline value for odour annoyance, indicating further work may be needed to achieve permit compliance