Revealed – the hard task of countering a concreteberg

Wastewater engineers from Lanes Group plc are working with colleagues at Thames Water to keep water flowing around a giant ‘concreteberg’ blocking a sewer in North London.

The giant plug of concrete, thought to be up to 100 metres long and weighing up to 105 tonnes, the same as a blue whale or 20 elephants, was discovered by a Lanes CCTV survey team in Goswell Street, Islington.

It was christened a concreteberg after fatbergs – large blobs of fat, oil and grease (FOG) and wet wipes that also regularly block urban sewers – and is the largest mass of the building material ever found in a London sewer.

Lanes, the wastewater network services maintenance partner for Thames Water, has put in place an emergency sewer monitoring and maintenance programme to protect local homes and businesses from sewer flooding.

Andy Howard, Special Projects Manager for Lanes, is leading a team of up to 13 wastewater engineers who have been selected for their skills and experience in tackling blockages in trunk sewers.

He said: “The concrete is blocking a 100-metre section of main sewer in one of the busiest parts of London. We had to urgently find a way to divert wastewater flows around it.

“Otherwise, the sewage would start to back up and there would be a serious risk of flooding in homes, businesses and roads around the blockage and potentially for quite a distance behind it.”

The emergency concreteberg response team is made up of a seven-person confined space entry team, which includes two rescue personnel, all qualified to use breathing apparatus, a jet vac tanker team, a CCTV drainage survey team and two managers.

A parallel team of Thames Water sewer network engineers and specialists are also working on the project to support Lanes and identify the best way to clear the concrete which is stuck fast to the walls of the 1.2-metre-high brick-lined Victorian sewer.

Andy Howard is part of a special projects team established by Lanes to support Thames Water on complex tasks, both planned and reactive, that need a flexible response and specific mixes of skills to implement and complete successfully.

In many cases, they will be working closely with Thames Water counterparts on projects that have an element of urgency or are vital to the strategic objectives of Thames Water’s wastewater network programme.

Projects can include emergency responses to potential pollution incidents and major sewer blockages (as with the concreteberg), investigations into suboptimal sewer performance, and planning for major changes to sewer lines or treatment facilities.

Lanes Technical Director Andy Brierley said: “We have the skills and capacity to put the right special teams in the field to complete the most challenging tasks. Determination and the ability to think around seemingly intractable problems are key qualities.”

In the days after the concreteberg was discovered, in the second week of April 2019, Lanes personnel used robotic cameras and sewer walks to survey 550 metres of sewer to assess its impact on the local drainage system.

They then cleaned 350 metres of main sewer. This included the 230-metres of the Moreland Street local sewer that connects the Goswell Road sewer with the London Bridge main line sewer, which runs parallel to it.

“By cleaning the Moreland sewer, we ensured it had enough capacity to divert sewage into the London Bridge sewer,” said Andy Howard. “This is giving Thames Water time to assess how to remove the concrete, which is going to be a major task.”

An estimated 600 litres of sewage per minute is being diverted down the Moorland sewer. Andy Howard explained: “We are now having to inspect the sewers twice a day to make sure the sewage is getting through, and we will have to carry out a full clean of the system, probably every week, until the concrete is removed.

“As this incident shows, the response we have to put in place to protect the local community and restore the sewer system after blockages like this is often extensive, time-consuming and very costly.

“On top of that, our teams face the hazard of having to enter large sewers and wade through sewage that may reach their chests to respond to the emergency, which is something we want to avoid.”