Alternate: Retire or Rehab? Optimizing existing wastewater and collection system facilities to improve resiliency

Purpose: This paper will illustrate how one City used strategic planning tools to improve system redundancy and resilience through optimal use of existing infrastructure and strategic capital improvement investments. Benefits of Presentation: Attendees to this presentation will learn methods for integrating climate change and resilience into long-term planning. Attendees will also be able to describe the challenges associated with applying existing planning assumptions that have not been updated to reflect changes in construction practices and improved water conservation technologies. Finally, attendees will learn how the City is phasing the improvements to meet future growth and balance funding priorities. Abstract: The City of Daytona Beach's (City) wastewater collection system serves more than 80,000 customers on Florida's Atlantic coast. This system is now facing rapid growth and expansion in tandem with new development, particularly in the western portion of its service area where the flows are treated by the Westside Regional Water Reclamation Facility (WRWRF) (permitted capacity of 15 million gallons per day). Meanwhile, the eastern portion of the City, which is experiencing minimal growth and re-development, is primarily served by the 13 mgd Bethune Point Water Reclamation Facility (BPWRF). In the past, the City considered retiring the BPWRF because of its vulnerable coastal location and limited space for expansion, in combination with its renewal and replacement (R&R) needs. However, the City's 2020 Wastewater Master Plan raised concerns regarding the near-term treatment capacity of the WRWRF and redundancy/reliability for emergency situations. More specifically, the City's population was projected to increase by 93 percent through 2040, particularly within the WRWRF's fast-growing service area. At that rate, the City's wastewater flows are projected to more than double from 12.6 mgd to 26.1 mgd with most of this increase to be treated at the WRWRF. At the rate estimated within the master plan, the capacity of WRWRF would be exceeded by 2025. Meanwhile, wastewater flows to the BPWRF were projected to be less than 6 mgd through 2040. In other words, the BPWRF has excess permitted treatment capacity, as well as infrastructure, that could be utilized to also serve a portion of the WRWRF's service area if the City were to consider flow diversion. As it currently exists, the City's collection system is equipped with the operational flexibility to temporarily divert flows from the WRWRF to the BPWRF through existing piping and a master re-pump lift station. A permanent diversion requires replacing an existing 16-inch/24-inch force main with a 30-inch force main and significantly rehabilitating the BPWRF's assets; however, it will allow the City to shift approximately 5 mgd from the WRWRF to the BPWRF to maximize the use of the City's existing infrastructure and free up capacity at the WRWRF to reliably serve near-term growth. With this potential in mind, the City conducted a flow diversion study that examined the most cost-effective solution for the City's future capacity needs. This study centered around the evaluation of three potential scenarios, which accounted for different alternatives: - Scenario 1, No Change: Expand the WRWRF to address future growth while maintaining the BPWRF. - Scenario 2, Full Diversion to the WRWRF: Divert all flow from the BPWRF to the WRWRF, expand the WRWRF, and retire the BPWRF from service. - Scenario 3, Partial Diversion to the BPWRF: Divert selected lift stations from the WRWRF to the BPWRF and extend the WRWRF's operation to serve new growth while delaying expansion. After assessing each WRF's condition and limitations and completing hydraulic modeling of the collection system under the potential scenarios, Scenario 3 Partial Diversion was the most feasible alternative in optimizing the City's available treatment capacity, safeguarding flexibility for diversion between two plants during emergencies, and protecting historical capital investments made to the BPWRF, all at the lowest planning level comparative cost. With this study, the City developed renewed rehabilitation goals for the BPWRF, which focus on reinforcing its equipment and infrastructure's resiliency to elevated design standards to protect against sea-level rise and extreme wet weather events. Status of Completion: The Master Plan was completed in 2020. While development is occurring at the pace projected in the Master Plan, flows are lower due to better conservation practices and technologies in the new construction. However, the City is still anticipating the need for these facilities, and has been actively implementing strategies outlined in this plan. Design and construction of critical infrastructure to complete the diversion is underway, including rebuilding a pump station and upsizing a force main. Work will soon begin on improvements to the BPWRF so that it can receive and treat the additional flows. A This presentation reviews the process by which the City balanced the complex and often opposing needs of two WRFs at either end of an extensive wastewater collection system; one (the WRWRF) struggled to keep up with growth in a newer, sprawling suburban area while the other (BPWRF) had unused capacity but significant rehabilitation needs. The flow diversion study and its final recommendation exemplify how a single strategy can maximize the strengths and meet the needs of both WRFs while setting off a chain of clear-cut, prioritized capital projects that cohesively work towards overall system optimization, resiliency, and redundancy.