Modern Master Planning in South Florida: Resilience and Condition Assessment Considerations for Regional Wastewater Transmission

Our presentation will summarize the importance of incorporating resiliency and condition assessment into regional wastewater master planning to develop a balanced long-term capital improvement plan. The plan addresses traditional master planning considerations such as growth, hydraulic capacity and level of service, but also addresses asset condition, remaining useful life of critical assets, and system resiliency. Broward County Water and Wastewater Services provides drinking water for 59,000 customers while serving as a regional wastewater authority for over 600,000 residents in South Florida, with treatment at its North Regional Wastewater Treatment Plant. The plant and the regional transmission system are presented in Figure 1. The regional system is a pressurized transmission system receiving wastewater from both local systems and large wholesale customers, with eleven master pump stations that serve multiple gravity collection systems. The root need for the master plan is to address the aging infrastructure in the regional system and ensure reliable service for both the local and wholesale customers. While traditional master planning activity including hydraulic modeling and capacity assessment were performed, the traditional evaluation was augmented by the following modern master planning activities:
1. Condition assessment of the eleven master pump stations was performed for individual architectural, structural, building mechanical, process mechanical, and instrumentation and control assets. Figure 2 presents the asset score for one of the pump stations, with lower scores assigned to better asset conditions. As shown in the figure, the pump station was evaluated on nearly eighty individual assets to develop specific recommendations for each key asset in the station.
2. The hydraulic capacity assessment included a system resiliency evaluation to determine which branches of the transmission system have adequate redundancy in the event of a main break, and which branches can be more reliably served with a parallel relief main. In the example presented in Figure 3, a transmission main break downstream of four master pump stations can be mitigated by a regional relief main to the east. The evaluation determined that the majority of the central system has adequate redundancy to maintain service in the event of a break, following the installation of isolation valves to route the flow to the Northwest plant via one of the looped mains.
3. Transient modeling was performed to identify potential hydraulic issues from a sudden shutdown of a master pump station. In the example presented in Figure 4, the addition of a combination air and vacuum valve can mitigate the potential for vacuum conditions in the transmission mains following the sudden shutdown of the pump station.

From the elements of the planning process, a capital improvement plan that addresses hydraulic capacity, transient mitigation, asset condition, and resiliency was developed for the County's long-term implementation. By addressing each of these elements together, the plan is holistic and adaptable as the County moves forward. At the time of this abstract, the condition assessment, hydraulic modeling, transient modeling, resiliency analysis, and capital improvement plan development are final and complete. The overall master plan will be complete by November 2020. Our presentation will benefit any wastewater utility that is in the master planning process or considering developing or updating their master plan. While the case study is applicable to any wastewater utility, there will be additional benefits to any utility that operates regional transmission mains or manifold force mains with multiple pump station inputs.