Optimised Long Term Condition-Based Renewals of Hastings District Council Trunk Sewers

It is every wastewater asset owner’s desire that their wastewater systems should operate with minimum or no interruptions (Beardi et al, 2008). Hastings District Council (HDC), who own over 400 kms of wastewater pipeline assets and historically used the age-based approach for sewer rehabilitation, have adopted a new optimization strategy to improve its sewer renewal programme from a value for money perspective. Patterson and James (2007), and Ali and Schofield, (2017) presented the application of facets of this new approach to small diameter reticulation and large diameter pipes at Clive Wastewater Treatment Plant (WWTP).

A key feature of the strategy is the two stage approach; Level One involving the determination of condition-based residual life and programming for rehabilitation or further monitoring followed by Level Two targeted at optimizing the prioritization of short term (<5 years) repairs using risk matrix scoring. This paper focuses on the recent application of the new strategy to HDC trunk sewers and features the following:

• Outline of optimized framework for trunk sewer renewal.
• Criticality-based framework for identification pf asset groups targeted for rehabilitation
• Condition investigations including; CCTV inspection, laser/sonar clear and objective profiling, and pipe coring.
• Visual scoring system based on the extent of internal surface corrosion.
• Progress to date on trunk sewer condition assessment and rehabilitation
• Program of renewal, replacement and on-going inspection proposed over the next 10 years.

The adoption of this trunk sewer renewal strategy allowed HDC to unlock value from their assets by utilizing them to the end of their real of life whilst remaining vigilant to mitigate the risk of catastrophic failure in service. More importantly, the funding requirements have been evened out, in contrast to age- based replacement where the renewal of large portions of the trunk sewers would coincide within a small 10-20 year window period.