An exhaustive evaluation of capital improvement alternatives for a wastewater catchment in western Newcastle was performed using Optimizer. While there were a number of potential variables in the upgrade of the system, including conveyance solutions, I/I rehabilitation, storage and WWTP upgrades, one alternative that was consistently identified as a best value option was linear storage (or inline Flow Control Facilities – FCFs).
The catchment area services a population of approximately 20,000 and there is limited capacity in the existing collection system gravity mains and pump stations. Based on 10-year long term rainfall simulation of the existing system, environmental discharges occur at a two-week average recurrence interval (ARI). The primary target level of service for the catchment is an ARI of less than one overflow event every three months.
The Newcastle wastewater optimization project involved the following tasks:
- Options identification workshop
- Unit cost rate development
- Design storm selection
- Preparing alternatives in the hydraulic model
- Defining the design and performance criteria
- Formulating the optimization model and performing optimization runs
The optimized (least-cost) Solution for the 3-month ARI design event is characterized by inline FCFs (providing a combination of stormflow conveyance capacity and up to 3 ML of instantaneous attenuation capacity), branch sewer upgrades and a pump station upgrade.
The cost-effective analysis curve shown above compares each solution generated from the optimization scenarios performed for the 3-month design storm scenario. It shows how total project costs and individual cost components change with respect to the maximum flow discharged from the catchment for the 3-month design storm event. The Optimized Solution (Scenario 1A) was approximately 50% lower in cost relative to the Conveyance-Only Scenario and approximately 20% lower in cost relative to the scenario with maximum discharge to the WWTP constrained so as not to exceed the existing pump station capacity (Scenario 1C).