Optimizing a Collection System to Address Future Uncertainty; Applying Real-Time Controls to Mitigate the Effects of Rapid and Unprecedented Growth

Overview Over the last few years, Gwinnett County GA, has experienced significant population growth and by 2040, Gwinnett County is projected to become Georgia's most populous county with approximately 1.5 million residents, which represents more than a 50 percent increase from today. Future planning for the sanitary sewer system is challenging. To overcome these challenges, the Gwinnett County Department of Water Resources (GCDWR) developed a comprehensive, countywide sanitary sewer model database to facilitate a holistic system evaluation. Using the countywide model, GCDWR identified short- and long-term solutions that provide flexibility to meet future needs while offering strategies to address uncertainties in growth. The goals of this analysis are to provide flexibility to accommodate new development and redevelopment and maintain appropriate levels of service without the costly burden of unnecessary capital improvement projects. This paper examines the implementation of Real-Time Control (RTC) at existing flow diversion structures, which is a key strategy associated with the potential solutions. The RTC implementation facilitates an adaptive management approach to flow control. When necessary, flow diversion can be introduced during emergencies or maintenance activities. The RTCs allow GCDWR to maximize the use of existing infrastructure by actively balancing flow between water reclamation facilities (WRFs); thereby eliminating the need for increased conveyance and treatment capacity in the western part of the County. It also will allow for increased flexibility to adapt to the rate of population growth in the event that it differs from current projections. Approach, Results, and Current Status GCDWR's key tool for the strategic planning is a countywide hydraulic model of the sanitary sewer collection system. This countywide model allows GCDWR to evaluate the potential benefits of balancing flow between the existing WRFs. GCDWR conducted a comprehensive evaluation using the countywide model to determine a range of different improvement combinations and the sequencing of those improvements for the next 25 years. These improvements consist of WRF expansion, deep conveyance / storage tunnel, RTC to balance flow between two WRFs, upsizing interceptors, and pump station upgrades. Over 50 improvement combinations were evaluated and resulted in five recommended solutions for leadership consideration. Figure 1 shows an example roadmap of the solution alternatives and the corresponding phasing plan. This evaluation is completed, and GCDWR leadership has been using this framework to combat the uncertainties in growth. Benefits and lesson learned The benefits and lessons learned from this analysis include: 1.Collaboration among key personnel provides a holistic understanding and establishes a common vision regarding how the future demands can be met with different alternatives, while maintaining an acceptable level of service. 2.Flexible solutions are important during uncertain times and must be integrated into the management strategy to accommodate unforeseen situations and implement viable system upgrades as well as capital and operational projects. 3.RTCs can provide significant savings in capital investments as these controls can be used as a temporary solution to delay projects or as a long-term solution to eliminate future infrastructure needs. 4.Engineering and operations staff must be engaged during the planning stages as the implementation of preferred strategies requires buy-in from both groups. 5.Open communication and mutual understanding between the planning, financial, and operations teams is necessary to overcome challenges associated with competing demands and meet the overall organization goals. Conclusion A comprehensive strategic plan with multiple solution options and alternative paths is the key to navigate unpredictable conditions. Planning efforts to date have resulted in a flexible management framework for GCDWR to mitigate uncertainties regarding future growth.