Thames Water has launched what it expects to be a lengthy operation to remove a mass of concrete discovered to be plugging three Victorian sewers.

Caused by people pouring concrete down their drains, this blockage is expected to be far more difficult to remove than the fatbergs, collections of fat, oil, and wet-wipes, more commonly seen.

In November 2017, Thames Water took nine weeks to clear the infamous Whitechapel fatberg and commemorated the event last year with a “special edition” manhole cover.

The work, starting next week at the junction of Gosling Road and Hall Street in Islington, London, is expected to last for at least the next two months. The blockage is the biggest the company has seen of its kind, estimated to be a minimum of 100 metres long and weighing in at 105 tonnes, within the weight range expected of a blue whale.

The operation will utilise a range of cutting tools, such as jackhammer pneumatic drills and high-pressure jets, to chip the set concrete away from the Victorian brickwork. Tankers will be on standby 24 hours a day to pump out waste and protect the environment as well as nearby properties and businesses from flooding. This is all is expected to cost at least several hundred thousand pounds.

Every year Thames Water, with a customer base of 15 million, spends £18 million clearing blockages from its sewers. The company stressed that this money could be better served investing in the network or helping vulnerable customers.

Alex Saunders, Thames Water operations manager, said: “Normally blockages are caused by fat, oil and wet wipes building up in the sewer but unfortunately in this case it’s rock-hard concrete. It’s in there and set to the Victorian brickwork, so we need to chip away at it to get it removed.

“This is not the first-time damage has been caused by people pouring concrete into our sewers but it’s certainly the worst we’ve seen. It’s very frustrating and takes a great amount of time and effort to resolve. We’re now doing everything we can to deal with it as quickly as possible, making sure our customers don’t have to suffer because of this mindless abuse of our network.”

The water industry is taking steps to educate the public on what can and cannot be flushed in its fight against sewer blockages. Earlier this year Water UK created a “fine to flush” symbol to help consumers identify products, such as wet wipes, which could be safely flushed.

An investigation into the source of the concrete is currently underway, with Thames Water hoping to recover some costs from the culprits.

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