Just being completed on probably one of the most challenging building sites in the UK, is a project to construct a sewage screening station, located in an isolated cove on the outskirts of Polperro, together with a 330 metre long pumped sea outfall extension.
The project, being carried out by Dean & Dyball, is one of South West Water’s current major projects, with another project comprising the construction of a £3 million new service reservoir, being undertaken by Balfour Beatty, near Newquay in Cornwall.
At Scilly Cove, Polperro, the site is situated with sheer cliffs to the rear, the sea to the front and accessed only by stone steps and a cliffside path. This means that the construction site is serviced solely by sea. To facilitate construction work, a temporary steel working platform was erected to support a 100 tonne crawler crane.
The screening building was constructed from modular precast concrete sections. This system is quick to erect and 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 project also involved the construction of a 330 metre long outfall pipe assembled as a single section in Par Docks, with a concrete weight jacket having been 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 sunk into a pre-excavated trench.
So that South West Water can maintain the facility, an access lift was built from the coastal path to the screening building at the base of the cliff – 23 metres below. This necessitated profiling of the cliff to a constant gradient and a discreet system of rails to give a ‘shaftless’ design. When not in use the lift car will park inside the screening building.
The new, covered, reservoir near Newquay is being built next to the existing Coswarth service reservoir at Quintrell Downs. It will replace the existing reservoir, parts of which date back over 100 years, which is reaching the end of its useful life.
When it is finished, it will store treated water from Restormel Water Treatment Works and supply 9,000 homes in Newquay and the surrounding area with top quality tap water.
At 62 metres long, 32 metres wide and eight metres deep, the reservoir will hold 13 megalitres (13,000,000 litres) of water – enough to fill five Olympic-sized swimming pools.
The reservoir is being constructed using 680 tonnes of steel reinforcement and 2,700 cubic metres of concrete. Fifty reinforced concrete columns will support the reinforced concrete roof.
The project is due for completion in March 2012.