Civil engineering, infrastructure and tunnelling specialist Barhale has been selected by Thames Water to deliver a £21m strategic investment in the Thames Water Ring Main (TWRM) in West London.

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 resilience of supply in the west of the capital.

Once operational, the Mogden Pump out Shaft (HPOS) will be able to supply the whole of Thames Water’s Hampton area, which includes parts of West London, Kingston-Upon-Thames and Twickenham postcodes, at close to the normal operating pressure in the event of a failure at Hampton POS. More than 300,000 people take their water from the local network fed by Hampton Water Treatment Works.

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 108 Ml/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 33″ 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 x 3,8 MVA HV metered supply power supply, drawing from a network independent of that used by Hampton Pump Out Shaft, to provide additional protection from electrical supply failure.

The Mogden Inspection Shaft is located in a separate compound in the North West corner 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 existing 38m deep shaft.

Shane Gorman, Barhale’s Water Director explained that a number of considerations had to be overcome when shaping the design solution.

“At 7m the Mogden shaft is a narrower diameter than the 10m typical for a pump out shaft.” he said. “So our design had to reflect the reduced available space. Additionally, this is 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 Ring Main dating back more than thirty years. Recently, we have completed extensive 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).”

“We are very pleased that Thames Water has chosen us for this important strategic investment which will provide crucial reinforcement to the water supply in West London.”