The goal of this case study is to demonstrate the application and utility of a developed System Dynamics (SD) model to assess the sustainability of strategic decisions for managing the wastewater collection (WWC) pipe network system for a medium-size municipality in Southern Ontario. Two asset management scenarios, suggested by the research-partnered municipality, are adapted based on the acceptable maximum fraction of pipes in the worst condition (ICG5) being equal to (1) 10% of the network-length/year, and (2) the initial 2.8% of network-length/year for the entire life cycle of the asset. The urban densification scenarios are restricted to a 50% urban densification rate. The least maximum rehabilitation rates of 1.41% and 1.85% of network length/year are found necessary to keep the ICG5 pipes fractions below the selected 10% and 2.8% thresholds, respectively. The maximum and minimum user fee-hike rates for WWC and wastewater treatment (WWT) services are adjusted to support the financial self-sustainability aspect. Results from the SD model, as presented over a 100 year simulation period, show that an accelerated rehabilitation strategy will have a lower financial cost with the lowest greenhouse gas (GHG) emissions. This study highlights the implications of integrating asset management of wastewater-collection and -treatment systems. Applying such an integrated SD model will help decision makers to forecast the future trends related to social, economic, and environmental performances of wastewater infrastructure systems, and evaluate the behavior of interrelated and complex WWC and WWT systems to find synergistic cost-saving opportunities while at the same time improve sustainability. Systems 2019, 7, 34 2 of 17 Systems 2019, 7, 34 3 of 17volume and changing the wastewater composition at the WWT plants. They also showed that the increased operational and capital expenses at WWT plants can reinforce the deterioration of WWC systems through the interconnected socio-economic system. Goal and Scope DefinitionThe goal of this case study is to assess the sustainability of strategic decisions for managing the WWC pipe network system for a medium-size municipality in Southern Ontario. The main attribute of the strategic asset management decision is the 'acceptable maximum fraction of WWC pipes in worst internal-condition grade' or ICG5-based on the UK-Water Research Center (WRc) [10] condition-grade rating system. This policy lever was introduced in Rehan et al. [5] to control the level of service or performance of the WWC system.The subordinated policy levers, such as maximum rehabilitation and user fee-hike rates, should be adjusted to continue provision of WWC, as well as, WWT services within the financial self-sustainability paradigm. The finance strategic decision is simplified to the pay-as-you-go strategy only. Borrowing or capital reserving options are not included in this assessment.The three indicators listed below are selected respectively from the financial, social, and environmental sectors for sustainabili...

This paper presents the development of a novel system dynamics (SD) model for better understanding the interrelation and feedback mechanism between the wastewater collection (WWC) and wastewater treatment plant (WWTP) systems. Causal loop diagrams (CLDs) are developed and discussed to depict and understand feedback and inter-connections between physical, financial, and consumer sectors. The developed SD model is then extended to include the greenhouse gas (GHG) emissions, as a proxy for the environmental sector and for an environmental sustainability assessment of strategic decisions related to asset management planning of wastewater infrastructure system. It also adds new policy levers, such as population growth and urban densification in the social sector, and minimum fee-hike rates in the finance sector to enhance the representation of real-world conditions in the asset management planning. This new SD model will enable decision-makers to assess the sustainability impacts of their strategic decisions on wastewater systems, find synergistic cost-saving opportunities, and improve the sustainability performance of their asset management plans.

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Developing socially acceptable, environmentally friendly, and financially viable asset management plans (AMPs) is a major challenge for water and wastewater utilities and calls for a comprehensive Sustainability Assessment (SA). This paper proposes a novel framework that applies System Dynamics and Life Cycle Assessment tools to evaluate the long-term sustainability of strategic asset management decisions for water and wastewater infrastructure systems. The merit of the proposed framework in dealing with the non-linearity and dynamic behavior of the socio-economic systems and its utility for SA of strategic asset management decisions are demonstrated in a case study of a Wastewater Collection (WWC) network system. Furthermore, the significant importance of population growth and urban densification policies in sustainability of AMP are highlighted by comparing four alternative scenarios of (1) 100% urban densification, (2) 0% urban densification, (3) 50% densification, and (4) no population growth in the case study. The results of the case study show that the greenhouse gas emission, operational and capital expenses, and bill burden of WWC and treatment services significantly reduce with urban densification.