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Going underground to inspect new sewer system

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From a distance, United Utilities’ terminal pumping station in Penwortham looks just like any other farm building.

But up close, the sheer scale of the water giant’s works becomes clear - especially when you’re looking 30 metres down a shaft which resembles a huge underground cathedral.

Engineers will have been working on the landscaped site for four years this March, as part of a vast £160m scheme to enhance Preston’s sewer system.

Enormous pipes, wide enough to drive a car through, and storage tanks the size of Olympic swimming pools have been carved out deep underground.

They connect the old Victorian network beneath Preston with a new network, passing under the River Ribble to the pumping station off Howick Lane.

There, giant pumps lift flows from the tunnel via twin rising mains, before the water crosses under the river again to Preston Wastewater Treatment Works.

During heavy rainfall once the sewer pipes are full, stormwater which previously would have spilled into local watercourses will now be diverted into a new 3.5km long underground tunnel, capable of holding 40 million litres of stormwater.

When the heavy rain stops, this stormwater will be pumped back into the sewer network, where it will go on its journey through a maze of pipes to the treatment works at Clifton Marsh.

There it will be cleaned until it is of a safe standard to go back into our rivers and seas.

Carl Sanders, senior project manager, says: “This is a massive engineering project and we’re doing it for an environmental reason, that is the great thing about it.

“It’s all about the River Ribble and the bathing waters off our coast and making it look as good as it can.

“We’ve got the river just behind us and before we did our work floods from Preston used to go in there.

“Now we’ve constructed a water storage system to prevent that and we’ve built it so it will only spill to the Ribble a maximum of three times during the bathing season and 10 times a year.”

The site became active on December 17, yet despite all the rain and high water levels so far this year, the system is yet to spill to the river.

And when it occasionally does, Carl says the water will have first passed through a castellated weir, where all the debris is broken down in four slats like giant “cheese graters”.

Carl says: “In a heavy storm, the flow keeps coming and we can pump up to 1,500 litres of water per second to Preston Wastewater Treatment Works.”

Construction manager Nick Sharwin says it is hard to get across to people the “sheer scale” of the site and the work completed underground, which at the pumping station began by carrying out a massive dig.

Concrete, metal sheets and steel fixings were all delivered by wagons to the site, with workers battling against difficult wintry conditions, and at times working through the night.

He says: “In 2010, it was about -14°C and we were really struggling to pour the concrete because it wanted to freeze, so we had to use heaters to keep it at the right temperature.

“When we were working in the shaft we were quite lucky because you have a normal ambient temperature underground.

“We utilised all the excavated materials for the embankments we’ve built around the site. It has all been landscaped to look like farmers’ fields.” The site will be maintained on a regular basis, but it will actually become an unmanned operation, controlled by operatives at Clifton Marsh.

Carl says: “This isn’t something you build every day - it’s one of the biggest engineering works in Preston’s history.

“It’s extremely exciting when you’re working on something so beneficial for the local area.”

However, Carl is humble when describing the array of pipes and equipment installed by their team.

He says: “A lot of it is just the same as the plumbing you have in your house - just on a massive scale!”

The company says its ‘reliability testing’ has been a success and it is now ready to complete the final phase of work, to permanently connect the storm water tunnel into the existing live wastewater network. United Utilities is a partner of Love My Beach, a campaign which brings together various groups, including the Environment Agency, National Farmers Union, Marine Conservation Society, British Destinations, Keep Britain Tidy and local authorities, to keep the North West’s bathing waters clean.You can find out more information about how you can help reduce pollution getting into the sea, as well as find out how the organisations are working together, by going to www.lovemybeach.org.

 

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