Tunnel vision

Stuart Crisp demands clear, consistent sewer specifications to ensure that future generations are not left to pick up the pieces

The UK has one of the oldest and largest sewerage networks in the world. Over 40 per cent of it was built before 1945 and many parts are now in desperate need of replacement or repair. The December 2011 Water White Paper drew attention to the low levels of replacement for the public sewer network, noting that only 1 per cent of public sewers were replaced between 2000 and 2008.

Prompted by this, the Concrete Pipeline Systems Association (CPSA) reviewed the figures submitted to Ofwat by water companies between 2006 and 2010. It calculated that an annual average of less than 0.2 per cent of sewers were renovated or replaced during that five-year period. If this rate of replacement continues, any new wastewater pipeline installed today will need to last for over 500 years before it is replaced.

An Ofwat study estimates the cost of replacing the 300,000km-plus sewerage infrastructure at more than £200 billion. This excludes the 200,000km of former private sewers and lateral drains transferred into water company ownership in October 2011.

With the need for such a long service life and prohibitive replacement costs, it seems sensible that any wastewater pipelines installed today should be capable of performing for a very long time.

Large diameter concrete and plastic pipes are used for most replacement and new sewerage systems. No product can be guaranteed to last the 500 years demanded by current replacement rates, but most will have a quantified design life. Design life can be defined as the length of time an element or system can be expected to perform satisfactorily before its anticipated performance falls below the original design requirements. From an economic perspective, design life is usually expressed as the time period over which an asset is depreciated, which means that if a concrete pipeline, for example, has been designed to last 100 years, the capital cost can be offset over this time.

It is never anticipated that a product will immediately cease to function at the end of its design life, so its service life also needs consideration. A sewer’s service life is defined by the CPSA as the period of time during which it will perform its primary function without requiring major renovation or replacement. Some loss of performance is acceptable.

To find out if the current rate of replacement is reflected in the specification criteria used by water companies, the CPSA asked them individually what design life they used to specify wastewater pipelines. Many specify a design life in excess of 50 years. However, it is not clear how rigorously this requirement is enforced. Neither is it clear how the service life (beyond the specified design life) of sewer pipes is considered in a water company’s design, specification and procurement stages.

The CPSA would like to see clarity and consistency in both sewer specification and enforcement from all water companies. These companies have a choice: to opt for a system that will perform well in the short term, while ignoring the implications for generations to come, or to invest in products that will provide the long-term performance demanded by the current replacement regime.

If water companies fail to consider service life in their selection of sewerage pipelines, we will be storing up a monumental problem for future generations. The CPSA is carrying out an intensive communication programme with these companies to help raise awareness of this issue.

Stuart Crisp, business development director for the Concrete Pipeline Systems Association.

More information on this issue can be found at: http://concretepipes.co.uk/files/Managing_Serviceability_24.05.12_000.PDF

This article first appeared in Utility Week’s print edition of 8th March 2013.

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