The Mogden pump out shaft scheme will upgrade the existing inspection shaft on the TWRM, the vital fresh water artery running beneath London, to provide additional supply resilience in the west of the capital.

Once operational, the Mogden pump out shaft will be able to supply the whole of Thames Water’s Hampton area, which includes parts of west London, Kingston-upon-Thames and Twickenham, at close to the normal operating pressure in the event of a failure at the Hampton pump out shaft. The Hampton Water Treatment Works supplies more than 300,000 people.

Four 350kW VSD pumps will be installed in the Mogden shaft. Each pump will be capable of delivering a peak flow of 36Ml/d (417l/s) to give a combined 108Ml/d (1250l/s) from any three of the pumps. They will be capable of being ‘turned down’ to meet current and future minimum night flows.

A new pipeline will be connected to the existing Kew 838mm main to the north of the site. A new surge column, surge tank, additional surge vessels and control panel will be installed on the outgoing connection.

Barhale will also install a 2×3.8 MVA HV metered supply power supply, drawing from a network independent of that used by the Hampton pump out shaft, to provide additional protection from electrical supply failure.

The Mogden inspection shaft is located in a separate compound of the Mogden Sewage Treatment Works site. The scheme will increase the footprint of the TWRM shaft compound to contain all new buildings, kiosks and ancillary equipment.

A new cover will be installed over the 38m-deep shaft.

Barhale water director Shane Gorman said the design had to overcome several challenges.

“At 7m the Mogden shaft is a narrower diameter than the 10m typical for a pump out shaft, so our design has had to reflect the reduced available space,” he said.

“Additionally, this is a clean water solution located within a sewage treatment works site so we have to put in place measures to mitigate and prevent any potential for cross-contamination. We do have the advantage of significant experience of the shaft and the ring main dating back more than 30 years.”

Barhale has recently completed inspections and replacement of the white caps along the two sections of the TWRM from the Kempton shaft to the Mogden shaft (6.875km) and from the Mogden shaft to the Kew shaft (4.820km).