Caisson style Vacuum Sewerage collection station.

Barhale's modular manhole construction.

Barhale Construction's revolutionary directionally drilled household sewer connection.

This summer Flowvac Environmental Ltd completed work on the United Kingdom’s largest vacuum sewerage system. After nearly 3 years working closely with Anglian Water and their partnering contractor Barhale Construction, 1500 properties in rural Cambridgeshire were connected to mains sewerage for the first time.

The decision to use a vacuum sewerage system for this scheme was due to the dramatic reduction in cost, risks and impact to both residents and the environment. When the scheme was first costed it was calculated that to install an equivalent conventional gravity sewerage scheme would have required the construction of 31 pumping stations and excavations to depths of 3metres or more. The resulting Vacuum sewerage solution involved the construction of just 4 Vacuum stations and 4 intermediate pumping stations, keeping designed excavation depths below 1.5metres throughout the scheme.

The shallow trenches and small bore pipe sizes meant that Vacuum sewerage was the perfect solution for an area characterised by a high water table, virtually flat terrain and poor ground conditions. Due to the shallow dig requirement of Vacuum Sewage Systems, less lorry movements, road closures and reduced contract times resulted in relatively little disruption to the local community. All of this coupled with the reduced backfill and spoil removal meant that the environmental impact of the scheme was also reduced.

Flowvac Environmental Ltd also worked with partners Barhale Construction and Anglian Water to introduce new innovations into the design and construction of the scheme. The collection stations were constructed using buried shaft caissons reducing safety risk and cost, the collection chambers were constructed using a similar 'sunk-shaft' method, improving construction times and reducing risk. The use of directional drilling in the construction of gravity lateral pipe work from households was also a new and exciting innovation pioneered by Barhale Construction for this scheme.

Perhaps the most significant development for Vacuum Sewage systems that was used extensively for this scheme was Flowvac Environmental's patented above-ground control pillars. Vacuum sewerage systems have traditionally placed all of the Vacuum sewage interface valve equipment in the collection chamber or a separate adjacent valve chamber. This method meant that the control and sensor equipment was always vulnerable to flood damage when old, leaky gravity sewers to which new chambers were connected or poor surface drainage resulted in prolonged flooding. Flowvac Environmental Ltd has pioneered the use of remote control systems situated in sturdy above-ground pillars which also has the added advantage of reducing the need for operatives to enter manholes to carry out routine service work. The scheme has already reaped the benefits with dramatically reduced system call-outs and a reduced maintenance programme.

The Upwell Outwell Vacuum sewerage scheme has also resulted in active debate about and review of the Anglian Water Vacuum Sewerage Specification. Working on such a large vacuum sewerage scheme, all 3 of the main protagonists; Anglian Water, Barhale Construction and Flowvac Environmental have worked to develop and review AW's specification for the construction of Vacuum sewage schemes bringing it right up to date for the future.