Beyond AMP8: Preparing the ground for Water Efficiency in AMP9
By: Joe Cahill
Read moreThe Storm Overflow Discharge Reduction programme represents the most significant investment in the water sector since privatisation. This initiative aims to mitigate storm overflow discharges, which are a common issue in urban areas where excess rainwater is released into water bodies, often leading to water pollution. The programme's comprehensive approach to sewer sealing and storm overflow management is crucial for maintaining environmental health and public safety.
Indeed, the recent winter rainfall in the UK has highlighted the vulnerability of areas to prolonged groundwater flooding and sewer infiltration. This phenomenon is particularly pronounced in regions with chalk geology, such as parts of the south of England, where the porous nature of the chalk allows for significant groundwater infiltration into sewer systems. During heavy rainfall events, this infiltration can lead to continuous discharges of highly dilute wastewater from overflows into rivers and other water bodies. This issue underscores the critical need for effective storm overflow management strategies, such as those outlined in the Storm Overflow Discharge Reduction programme, to mitigate environmental impacts and ensure public safety.
Operationally when these discharges occur there are only two immediate solutions; tanker the excess flows where feasible at huge cost or install some sort of limited treatment to minimise the impact with a regulatory acceptance of the partly treated discharge. Hitherto the Environment Agency has given water companies some leeway for these discharges through its Regulatory Position Statement 362 (RPS 362), which avoids prosecution for a limited period under certain conditions one of which is the implementation of an agreed infiltration reduction programme. However, RPS 362 is to be withdrawn in 2030 and any such discharges after then are likely to result in prosecution.
As a result, companies are embarking on unprecedented programmes of sewer renovation in high groundwater areas to reduce infiltration. Time is short and the renovation needs to work first time. Water companies therefore need to have confidence in the renovation techniques they select, particularly as they are often necessarily installed in less-than-ideal conditions due to the ingress of groundwater. At present the product standards (ISO 11296-4) does not include a test requirement for watertightness of the installed liner. If the liner is not watertight the result may lead to prosecution and the need for further potentially unfunded infiltration reduction works.
In response to an approach from a number of water companies, in 2025 WRc undertook a major collaborative research programme funded by water companies and lining system suppliers to develop a type test for lining systems. This built on some earlier work carried out by WRc about 20 years ago.
The lining system includes the liner and optionally also a lateral connection collar and there are now two leak tightness classes. The test method has now been approved by the Water UK Standards Board and is published as WIS 4-34-07 Specification for Leak Tightness Testing of Cured-in-Place-Pipe Lining Systems for Gravity Sewer Rehabilitation.
12 CIPP lining systems have now passed the WIS 4-34-07. However, using a tested system that has a test certificate is only the first step. There are several other steps companies need to take.
A test certificate is not an approval. The test was undertaken using the resin and carrier specified on the test certificate and installed in accordance with the manufacturer’s installation manual. If there is a problem with workmanship it may not come to light for many months or even years until the next high groundwater event, by which time it will almost certainly be impossible to prove that it was an installation issue.
a) Clients must satisfy themselves that the resin and carrier that the supplier are the same of those used in the product that was tested.
b) Ensure that liner is installed in accordance with the supplier’s instruction manual.
In the contemporary rehabilitation landscape, the role of the client’s clerk of works has been diminished, but their oversight remains crucial to ensure that installations, such as those involving liners, adhere to the manufacturer's specifications and industry standards. The absence of this traditional role necessitates alternative mechanisms to guarantee compliance and quality assurance. In many regions, quality control has become a paramount function, often overseen by third-party auditors who provide an independent assessment of the installation process. These auditors may conduct site visits, review documentation, and perform independent testing of samples to verify that the liner installation meets the required standards. Such practices are not only prevalent in some countries but are also increasingly recognised as essential for ensuring the integrity and longevity of infrastructure projects. The integration of third-party quality control schemes, which include rigorous testing protocols, serves as a safeguard against potential failures and ensures that clients can confidently rely on the workmanship of their installations.
The new SRM Sewer Renovation Design Guide (replacing the sewer renovation in the existing SRM) which will be published in August includes a new chapter on quality control including testing.