Leak free sewer repairs – tackling sewer infiltration through industry wide collaboration
By Peter Henley – Head of Pollution and Flooding Reduction
WRc has recently joined forces with the UK’s water companies and the sewer rehabilitation supply chain to work collaboratively in the development of an infiltration test methodology for determining what is a leak-free sewer repair.
Water companies in the UK are under huge public and political pressure to reduce discharges from sewer overflows. One of the major causes of discharge from sewer overflows is the infiltration of groundwater into sewer systems. During the next business investment cycle – AMP8 – water companies are, therefore, planning a major increase in the renovation of sewers to reduce this groundwater infiltration. However, their previous experience undertaking such works using some Cured-In-Place Pipe (CIPP) products resulted in inadequate resistance to groundwater infiltration.
Leak tightness is a functional requirement in standards covering drain and sewer systems (EN 752:2017 §5.1.9), and a basic requirement in repair standards and specifications, such as BS EN 13380:2001 and the WRc SRM Type 2 structural design method for sewer liners. However, each of these standards does not define a suitable test methodology to specify what is a leak tight repair, and neither do product standards.
WRc, along with Thames Water, Severn Trent, Wessex Water, Dŵr Cymru, Anglian Water, Government of Jersey and Southern Water have agreed to collaborate to define a suitable test method to ensure any procured cured-in-place-liner solution used during AMP8 can provide the right level of protection against ground water infiltration. To complete and refine this test method it was recognised that the supply chain would play a pivotal role in the process. Therefore, companies such as RSM, Applied Felts, Quadex-Lining Division, Lateral Repairs, Impreg, Inpipe, Onsite Central and Saertex are also participating.
The basis for the new infiltration test methodology is the CP308 test method (developed by WRc and partner water companies in 2008), which investigated the infiltration resistance of a number of CIPP liner systems then on the market. Four products were tested that met the then CP308 test criteria, but as several of these products are no longer available it was recognised by the industry that an update was needed to allow for a much wider range of products to be tested. It was also requested that the new method should become formalised into a Water Industry Specification (WIS), which may then form the basis of a BS EN standard in the future. The key elements required of the new test are the ability of any system to seal the ends of the liner, if it does not adhere to the host pipe; and the assurance that any lateral connections into the sewer after rehabilitation has occurred are also leaktight. This will mean that any system tested will include any end seals used and also, where appropriate, the method used to make good connections into the system.
The project has three main aims: to complete preliminary testing during the summer (2024); to refine the test methodology ahead of it becoming a WIS; and to ensure a range of products are assessed and available on the market as leak tight solutions for the beginning of the next AMP period in April 2025.
It is hoped that this collaborative project will provide the water industry with a wide range of liner products that can be used to tackle infiltration and help prevent CSO spills from groundwater infiltration. WRc will also provide an ongoing independent verification service using this new, clear test method for the supply chain either as a standalone product test or as part of the wider WRc Approved scheme. This will demonstrate the efficacy of the supply chains’ products for use in the UK and more widely.