Unblocking the sewers

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Friday 1st October, 2021

The environmental impact of blocked sewerage systems affects us all, with an increase in flooding in the UK and Water Companies in England & Wales, dealing with up to 300,000 sewer blockages per year, costing them around £100 million annually to clear them (Water UK, 2019) damages can be costly and life threatening.

The main culprits of blockages are fatbergs, made up from wipes and rags flushed down toilets and fat, oils and grease (FOGs) disposed in kitchen sinks have been widely covered in media campaigns to try to reduce the number of sewer obstructions.

What is less known about are pipe defects and poor sewer design, which the Manual of Drain and Sewer Cleaning identifies as pipeline location, layout and shape, defects and deterioration.

Most commonly used to clear the blockages is high pressure water jetting (WRc, 2020) followed by rodding or rotary drain cleaning.

EN 14654 and the Manual of Drain and Sewer Cleaning (2020) identifies two main units for use for sewer jetting, high-flow rate machines at pressures 100-200 Bar (1500-3000 psi) and low-flow rate machines at pressures 200-350 Bar (3000 to 5000 psi).

However, the Manual of Drain & Sewer jetting notes that when it comes to blockages, jetting units of the high-pressure low-volume type are usually employed (WRc, 2020). A number of jetting contractors (such as Lanes for Drains) also refers to high-pressure jetting at 3,000 psi in their websites, or publications, as the typical method to deal with fatberg related blockages (Lanes for Drains, 2021).

While many pipeline materials can be used to channel stormwater, surface water and wastewater, not all types of sewer pipes are suited to the same magnitude of water jetting pressure required to clear the pipeline blockage. EN 14654 warns that the maximum water pressure applied “will vary according to the pipe material, the condition of the pipe and type of nozzle”.

The Drain & Sewer Cleaning Manual identifies the status and condition of the sewer and certainty over the type of pipe material, with differing pipe materials having different levels of resistance to jetting. The Manual warns specifically against jetting damage to specific types of pipe materials, such as plastic and pitch fibre pipes, where damage in the form of small holes may occur and may be undetectable by CCTV.

Recent tests by the British Precast Drainage Association revealed that it could take as little as 3-5 seconds of jetting at high-pressure for some plastic pipe walls to fail.

Earlier versions of the sewers’ adoption guidance (Sewers for Adoption) used to offer addendums that would allow Water Companies to impose their own requirements. A number of Water Companies used to impose a minimum water jetting pressure of 4,000 psi for all pipes used in their sewer systems, removing the risk associated with damage during high-pressure jetting blockage clearance.

However, this requirement has been dropped in the latest Design & Construction Guide (DCG) adoption code. It is now the responsibility of cleaning contractors to manage the risk of pipe damage due to high-pressure water jetting during cleaning operations. The British Precast Drainage Association continues to believe that a margin of safety should be added to current plastic pipe standards bringing the current maximum water jetting pressure to 4000 psi (276 Bar) to limit the risk of damage and enable more efficient removal of sewers’ blockage.

For further information on the testing of pipe materials resistance to high-pressure water jetting by the British Precast Drainage Association please visit www.precastdrainage.co.uk/uploads/pdf/Jetting%20Test%20-%20Report%201%20(02.08.21).pdf

For more details on our pipeline solutions please call 01179 814500, email salesemail@marshalls.co.uk or visit www.marshalls.co.uk/commercial/civils-and-drainage/below-ground-drainage

References

Lanes for Drains (2020) Fatberg removal and cleaning. Lanes for Drains website: https://www.lanesfordrains.co.uk/commercial/services/fat-oils-and-greasedisposal/fatberg-removal-cleaning/

Water UK (2019) Fine to Flush – a major new development in the fight against fatbergs. Link: https://www.water.org.uk/news-item/fine-to-flush-a-major-new-development-inthe-fight-against-fatbergs/

WRc (2020) Manual of Drain and Sewer Cleaning. ©WRc, 2020

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