Risk based asset management for wastewater systems

Water and wastewater businesses set service standards that are concerned with structural integrity and operating condition of infrastructure, protecting and promoting the public health and ecological sustainability of the natural environment. But what are risk and asset management concepts when speaking about wastewater systems? Generally risk can be defined as the combination of the probability of an event and its consequences. In all types of undertaking, there is the potential for events and consequences that constitute opportunities for benefit (upside) or threats to success (downside). In the water and wastewater field, it is generally recognised that consequences are only negative and therefore the management of structural and hydraulic performance risk is focused on prevention and mitigation of damage. The potential impacts from water and wastewater line failures should be assessed on a system-wide basis. The goal is to identify those areas of the system that will have the most impact if a failure occurs, and focus asset management resources to manage the risk. A critical component of risk based asset management strategies is statistical and physical/probabilistic failure models which are needed to allow to reduce costs while providing a specific level of service: therefore condition assessment is required. The established condition level of the collection system is left to the discretion of the individual utility. Whatever benchmarks are chosen, they should refer primarily to the physical condition of the system and its components. In the past, and somewhere now too, the network management was based on a reactive approach. A proactive and preventive repair strategy for urban drainage systems is often more cost effective than the traditional approach of reactive sewer maintenance. At the same time multicriteria decision support have been developed by researcher. That data-hungry systems while promoting data collection, were also taking advantages from the increasing data availability. The 5th Framework programme of the EU supported research centres in developing integrated software dealing with public sewer and storm water networks of any dimension. The creation of new software started all over Europe. The ultimate product have been Decision Support System (DSS) to enable municipal engineers to establish and maintain effective management of their sewer networks. Software, like the ones of the CityNet cluster, include analysis of problems caused by ageing, structural failures, inflow/infiltration, exfiltration (leaking) and insufficient capacity which can cause floods, pollution of receiving waters, pollution of ground water and soil, treatment plant impacts and increasing maintenance costs [4]. The ultimate output of the DSS is to provide the most cost-efficient system of maintenance, repair and rehabilitation of sewer networks, with the objective to guarantee security of sanitary sewage collection and storm water drainage in order to meet social, health, economic and environmental requirements. This has to be done within the context of integrated catchment management and the strategic objective of ensuring security of water resources. The circulation and application of these instruments to real case study’s increasingly highlighted how different priorities can have components with the same characteristics if operating in different conditions. It is not only the component performance driving the maintenance decisions but also the evaluation of damage produced by failures if occurring to that component in defined local constraints. Risk based asset management supported by condition assessment of wastewater systems and a cost evaluation of failure consequences from the utility managers point of view will be presented in the paper; in particular the risk based procedure to maximize planned maintenance and minimize unplanned maintenance in capital investment decisions will be described.