Rotten egg smell across Newport likely linked to river sediment

The team is working closely with other organisations including Natural Resources Wales (NRW), Dwr Cymru Welsh Water, Wales and West Utilities, Public Health Wales and neighbouring authorities.

They have also carried out city-wide odour patrols and assessments in response to reports from residents of sulphurous-like, or rotten egg, smalls.

Other measures included targeted visits to multiple potential sources and drone surveys to identify sources not visible from ground level.

A wide range of premises and sites have been ruled out, including the landfill site and businesses in the Docks.

The geographical spread of complaints across the city suggests it is unlikely to be a single fixed source.

The findings support a working theory that the odour may be linked to the release of hydrogen sulphide from tidal river sediment in the Usk/Ebbw estuary.

Decomposing organic material in anaerobic sediments can release the gas, particularly during low tide. This can be influenced by factors including wind direction and speed, atmospheric conditions, the natural breakdown of organic materials and possible secondary contributors such as sewer discharges.

Hydrogen sulphide can be smelt at extremely small concentrations before reaching levels that would trigger health concerns. The levels measured in the city by highly specialised equipment are at very low levels and do not indicate a risk to health. However, we do appreciate it is causing an annoyance to many people.

Officers are continuing to monitor daily and assess the data against tide conditions, wind, temperature and location.

Further joint river survey work is also being undertaken with NRW and a multi-agency team has been established to review all the findings. Any new intelligence about other possible sources will also be thoroughly checked.

Councillor Yvonne Forsey, Newport City Council’s cabinet member for climate change, said: “The small team that has been investigating these complaints, alongside their other work, has been working diligently to try and track down what is causing the odour.

“It is reassuring that it is caused by ‘natural’ processes linked with the rivers that run through Newport rather than an industrial or commercial site.

“Officers will continue the work that is needed to confirm this is indeed the source and rule out any other possibilities.”