ENGINEERS in Oldham are close to completing the biggest construction project that the town will never see.

A huge storm tank at Hathershaw measuring 25 metres across and 20 metres deep will soon be sealed over forever – leaving barely a trace of its existence.

But its impact on the ecology of the nearby River Medlock could be profound.

The Hathershaw tank is just one of a £46 million chain of sewer network improvements by water company United Utilities to transform water quality in Oldham’s much-loved river.

The six individual schemes between Alt, near Oldham, and Clayton, in Manchester, will prevent tens of thousands of litres of dirty water ending up in the river during heavy storms.

Together they vastly improve the capacity of the local sewer network while allowing greater volumes of waste water to be treated to higher environmental standard.

Project manager Lucy Barnes said putting the concrete lid on the Hathershaw tank would be a major landmark for the huge team of engineers working on the project.

She said: “It’s got a capacity of 5,400 cubic metres and standing at the bottom of it is quite impressive. Once it is covered over, you will hardly know it’s there but it will be doing a great job helping improve water habitats.

“Our River Medlock project is designed to improve the quality of the watercourse from its source above Oldham all the way to where it meets the River Irwell. The aim is to help meet the Environment Agency’s objective of improving the Medlock’s ecological value from a moderate condition to a good one.”

By the time the project is fully operational at the end of this year, United Utilities will have boosted storage at Hathershaw, Snipe Clough, Bardsley and Failsworth Wastewater Treatment Works, where the addition of a new state-of-the-art treatment process called Nereda has also improved the rate and quality of water being returned to the river.

Failsworth is now only the third site in the UK to be fitted with the pioneering Nereda system – all of which are in the North West. Developed in the Netherlands, it uses tiny granules packed with bacteria and requires less energy than conventional methods of treatment.

Since starting on site in early 2018, the company and its contractor Laing O’Rourke have planted dozens of trees at Dovestone reservoir to help offset the environmental impact of building work and created a brand new sensory Peace Garden at Hathershaw College to say thanks for their patience while building the tank.

All elements of the project are expected to be fully operational before Christmas, although it could be the end of March before all works are completely off site.