Rare butterfly puts water firm's plan to flight

A rare butterfly is helping a water company save half a million pounds off the cost of an expensive sewage scheme.

The presence of the endangered Durham argus butterfly on a clifftop at Horden, Co Durham, forced Northumbrian Water to think about how to avoid placing construction works on its habitat.

The alternative engineering works it came up with for building a pounds 9.4m tunnel and pipeline taking treated sewage effluent out to sea should end up being cheaper than the conventional method.

The caterpillars of the small chocolate and orange butterfly live on rock roses growing on the clifftop magnesian limestone grasslands of the Durham coastline.

The habitat at Horden, near Easington, is a government-designated site of special scientific interest, largely because of the butterfly's presence. But it also lies between a new coastal sewage treatment works and the sea.

In normal circumstances, the water company would have created a construction site on the clifftop and another down on the beach.

Engineers would have sunk a big vertical shaft down to sea level from the top of the cliff, then joined this to another below-sea level tunnel dug from the beach to take the effluent out to sea.

But the butterfly's presence made the company think twice about clifftop works, and it has decided to dig a longer, sloping tunnel from a construction site set 350m back from the clifftop, avoiding the argus's haunts.