Decision-support Tools for Managing Wastewater Collection Systems

Wastewater collection systems are an extensive part of the nation's infrastructure. As these systems become older, more preventive maintenance and renewal are required. For municipalities to cost-effectively plan, organize, and implement this effort, they require improved information on structural conditions, decision-making tools, operation and maintenance practices, and techniques for repair and rehabilitation. Data from exemplary European wastewater collection systems are potential sources of novel and efficient maintenance and renewal practices.Although a considerable amount of money has been spent trying to increase the knowledge about the structural condition of wastewater infrastructure, the knowledge is still very limited. Pipe age is a factor; however, it is usually a combination of several factors that causes failures and influences maintenance decisions, making the situation very complex. To effectively manage maintenance and rehabilitation programs, managers need a quantitative picture of the condition and performance of their systems. Conceptually, this quantitative picture can be generated through the selection of performance indicators (e.g., overflows⊘year⊘mile), followed by collection of the required data (e.g., overflows⊘year, miles of sewer), and computation of the performance indicator value (e.g., 0.3 overflows⊘year⊘mile). Performance indicator trends can be used to monitor conditions and performance within a system over time (e.g., increase in overflow rate over last 5 years) or over space (e.g., sub-system X overflow rate is 75% greater than subsystem Y) and between separate systems (e.g., system A overflow rate is 50% higher than a similar system, B). Managers can use these indicators to identify, quantify, and justify areas requiring increased or decreased labor emphasis. There have been several attempts, both here and abroad, to develop and apply performance indicators; however, benefits and associated costs of using them have not been well documented.This paper discusses European approaches for diagnosing and analyzing water and wastewater systems, and in particular the use of performance indicators and non-hydraulic models for predicting failures in these systems.