Making decisions for upgrading wastewater systems

Decision-making to determine the preferred way of upgrading or constructing new developments is becoming more complex. In the drive towards sustainability, the social, economic and environmental aspects now share equal weighting with the technical and cost-effective elements of each option. The process of evaluating trade-offs between, say, cost benefits and environmental or social disbenefits, has always been difficult, and it is now also important to demonstrate openness in decision-making, so that stakeholders can see the option selected is in fact the best possible within the constraints set. A simple multi-criteria approach, known as WISPS (wastewater integrated system performance score) has been applied in a theoretical study using actual data to decide which of four catchments in a Scottish water authority area should be prioritized for improvement. This approach follows closely the process which the engineers would use implicitly to make decisions, but has the benefit of formalizing the process, thus showing how these decisions were achieved. The robustness of the approach has been tested using two software packages: one for risk assessment (@RISK) utilizing Monte Carlo simulation; and the other, a complex multi-criteria decision support tool (ELECTRE). The more complex analytical approaches demonstrated that the simple WISPS method produced reliable results.