Storm Overflows in St Neot Reduced by 30% After Sewer Upgrades

Storm overflow spills in St Neot have fallen by 30 per cent after South West Water carried out upgrades to the village’s sewer network.

The improvements form part of wider efforts to strengthen the local wastewater system and tackle a long-standing issue with groundwater entering pipes.

Tackling groundwater infiltration

Engineers focused on preventing groundwater leaking into the sewer network, a problem known as infiltration.

When soil becomes saturated after heavy rainfall, pressure builds in the ground. If there are small gaps in pipe joints or manholes, groundwater can seep into the system. Although this extra water does not come from homes, it still travels to the wastewater treatment works, increasing the overall volume in the network during wet weather.

Charlie Ford, South West Water’s Project Manager for St Neot, said stopping that unwanted water entering the pipes was the first priority.

“At St Neot, a big part of the challenge was groundwater finding its way into the sewer network. When that happens across a number of pipes, it can increase the volume of water flowing through the system significantly during wet periods.”

Pipe within a pipe

Rather than digging up roads, engineers used trenchless repair techniques to carry out the work.

Around 200 metres of sewer pipe were lined internally, creating a watertight layer inside the existing pipe. Before the lining process, the pipes were cleaned using high-pressure water jets.

Charlie described the relining process as similar to building a new pipe within a pipe.

“It’s a way of strengthening the pipe without major excavation and when they’re sealed, groundwater can’t leak in through those cracks or damage caused by trees, unwanted objects, or animals.”

A number of manholes were also sealed to prevent water seeping through brickwork and joints.

Changes to pump operations

The way pumps operate at the site has also been adjusted with the installation of a new control panel.

Instead of sharp peaks and troughs in flow, the pumps now run more steadily. This smooths out pressure in the system and helps it perform more consistently during periods of heavy rainfall.

The impact has been gradual but measurable. Storm overflows in St Neot dropped by 30 per cent in 2025 compared with 2024.

Part of £16 million programme

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

As part of the next phase of work in St Neot, a further 900 metres of sewer pipe have now been surveyed. Engineers will use the findings to identify where additional repairs could further reduce the need for storm overflows.