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Trafalgar House (Tunnelling) has an estimated £8 million contract to design and build an undersea tunnel for South West Water's £60 million Penzance and St Ives sewage treatment scheme in Cornwall.The 2.6 km rock tunnel will run from Gwithian on the north Cornish coast to St Ives bay.The contract also calls for four diffusers at the seaward end of the tunnel.Treated wastewater will reach the tunnel outfall through a new 8 km pipe between Hayle and Gwithian.Work on sinking the tunnel shaft has just started and construction is scheduled for completion in late 1994.The tunnel is an important element of the total project, which is being constructed by the Trafalgar House Water Projects Consortium, comprising Trafalgar House Construction and John Brown Engineering.The project involves diverting exiting outfalls in the Penzance area and redirecting sewage to improved facilities at the new Hayle treatment works, before discharging through the new outfall as treated effluent.In all, the scheme calls for 25 km of pipelines ranging in diameter from 150 mm to 2,100 mm.Seven pumping stations also feature in the project. These will vary in capacity depending on the catchment area, which will include Penlee Beach, Wherrytown, Marazion and Bridge.The new treatment works will be built alongside the existing one and will use a submerged aerated filter system introduced into the UK by John Brown.