Balfour Beatty Civil Engineering Ltd

Polperro sewage treatment scheme

Client: South West Water

Value: £5.2 million

Dean & Dyball Civil Engineering, a division of Balfour Beatty Regional Civil Engineering, is responsible for the design and construction of a sewage screening station, located in an isolated cove on the outskirts of Polperro, and a 330 metre long pumped sea outfall.

Polperro, a tiny fishing village approximately half way between Plymouth and St Austell, has no vehicular access so the construction site of the screening station is serviced solely by sea. To facilitate construction work a temporary steel working platform has been erected to support a 100 tonne crawler crane.

This technically challenging and interesting project is in line with South West Water's expectations, bringing considerable benefit to the local community.

The screening building will be constructed from modular precast concrete sections. This system is quick to erect, minimises construction time and risks to the programme from adverse weather conditions. Pre-fabrication also gives a factory quality finish and allows incorporation of a rock texture and colour matching that will help minimise the visual impact of the concrete structure in this Cornish beauty spot.

The 330 metre long outfall pipe was constructed as a single section in Par Docks, with a concrete weight jacket being attached whilst the pipe is on land. Flotation pipes were strapped to the outfall pipeline to tow it into position, a distance of nine miles between Par Docks and Polperro. The pipe was then be sunk into a pre-excavated trench.

So that South West Water can maintain the facility, an access lift will be built from the coastal path to the screening building at the base of the cliff - 23 metres below. This will necessitate profiling of the cliff to a constant gradient, and a discreet system of rails will give a ‘shaftless' design. When not in use the lift car will park inside the screening building thus achieving a visually discreet solution.

The project is due for completion in summer 2011.

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