An overflowing sewage treatment works in Surrey is one of 250 sites that Thames Water identified as needing upgrading last year.
The Horley treatment works overflowed on Tuesday (2 January) during Storm Henk. Thames’ storm discharge and event duration monitoring map indicates that the storm overflow at the site is still discharging, some 38 hours after it began releasing sewage (as of 2PM on 4 January).
The Environment Agency has already said that it intends to launch an investigation into the incident after sewage spilled onto a public footpath.
An Environment Agency spokesperson described the spill as “completely unacceptable”.
They added: “We are aware of the ongoing situation at Horley Sewage Treatment Works which is completely unacceptable.
“We have recorded non-compliances against Thames Water for breaching their permit, and our officers are actively investigating this incident.
“We have also made clear that we require the water company to complete the previously recommended major infrastructure works for this site.”
Thames Water has apologised for the spill and confirmed that the site has previously been identified as needing an upgrade.
“We regard all discharges as unacceptable and are sorry to those affected by this,” the spokesperson said.
“We have published plans to upgrade over 250 of our sewage treatment works and sewers including Horley.
“This will improve the sites’ ability to treat the high volumes of incoming sewage and reduce the need for overflows during wet weather.”
The Horley site was named as one of 250 sites that Thames plans to upgrade as part of a £1.12 billion capital improvement programme.
This includes £650 million on enhancing and upgrading over 135 sites to improve resilience and provide extra capacity. Over the same period, Thames plans to spend £470 million on the wider sewer network.
At Horley, Thames said that an upgrade is needed at the works “to improve its ability to treat the volumes of incoming sewage, reducing the need for untreated discharges in wet weather”.
The scheme, which is still being designed, is due to complete in 2026.