Making decisions for upgrading wastewater systems

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