Cornish Village Sees Drop in Sewage Spills After Upgrades

Storm overflow spills in the Cornish village of Altarnun are falling following engineering work carried out by South West Water.

Altarnun Sewage Treatment Works, located on the edge of Bodmin Moor, was identified as one of the company’s highest spilling storm overflows in 2024, with 206 spills recorded. South West Water said action was needed and began work to address the issue.

Why the problem was happening

During periods of sustained heavy rain, the treatment works could become overwhelmed. This triggered the storm overflow system, which is designed to prevent homes and streets from flooding.

In moorland areas like Altarnun, groundwater levels can change significantly. This can lead to more surface water and groundwater entering the sewer network, putting additional pressure on the treatment works, particularly during wet weather.

Two-part solution introduced

South West Water carried out a two-part approach to tackle the issue.

To reduce the amount of water entering the sewers, teams conducted CCTV surveys to identify areas most affected by infiltration. They then installed a protective lining along 40 metres of sewer pipe and completed repairs across the local network, including upgrades to six manholes.

At the same time, a new storm storage tank was installed at Altarnun Wastewater Treatment Works. This increases capacity by allowing excess flows during heavy rainfall to be stored temporarily and returned to the treatment process once levels drop.

Spills fall by 20%

Following these improvements, the number of spills reduced by 20% in 2025.

Hazel Tranchant, Head of Tactical Asset Management at South West Water, said: “Customers quite rightly want to see storm overflows operating less often.

“At Altarnun, we’ve focused on reducing the amount of extra water entering the sewer network and increasing storage for rainfall so the system can cope better.

“We know there is much more work to do to reduce spills across the region but it’s great to see how targeted improvements like this are making a difference and that we’re heading in the right direction.”

Part of wider programme

The work at Altarnun forms part of South West Water’s £16 million Infiltration Reduction Programme. The programme targeted 175 high-risk sites after performance was reviewed across more than 1,600 storm overflows.

📷Hazel Tranchant in Altarnun