Bar Harbor Systemwide Conveyance Assessment: How Smart Controls Helped the Town Develop a Cost-Effective Solution to Meet CSO Mitigation Requirements

Introduction: The Town of Bar Harbor, ME (the Town), a popular tourist destination due to its proximity to Acadia National Park, operates four CSOs that discharge to Frenchman's Bay where water recreation is highly valued. The Town has two wastewater treatment facilities (WWTF); included in NPDES permits for the WWTFs are requirements for development, and periodic updates, of a CSO Master Plan to abate CSOs from the Town's four CSO outfalls. Bar Harbor prepared its first CSO Master Plan in 2006, the most recent update to the plan was approved by the Maine Department of the Environment (MEDEP) in 2021. The purpose of the CSO Master Plan is to identify abatement projects and intended implementation schedule to better control and reduce CSOs and to report on progress towards achieving those results. Project Overview: A systemwide conveyance assessment was conducted to evaluate the potential hydraulic performance for infrastructure improvements and infiltration/inflow (I&I) reduction projects identified in the CSO Master Plan and to develop a plan for other pump station, force main, storage and interceptor improvements needed to increase the system's hydraulic capacity, eliminate SSOs, and reduce CSOs to the levels of control identified in the plan. The CSO Master Plan's minimum level of control is a 1€year, 24€hour storm event producing 2.4 inches of rainfall as 'the benchmark by which alternatives are evaluated and cost€effective solutions identified.' Subsequent discussions with MEDEP in 2021 related to the West Street Pump Station (PS) CSO outfall (Outfall #007) and a feasibility study prepared in 2019, identified a 5€year, 24€hour rain event as the design storm for the solution(s). Out of the four remaining CSOs in the sewer collection system, the West Street PS CSO discharging to Eddie Brook is the highest priority for the Town's CSO reduction efforts based on potential impacts to public use and benefit of the receiving waters. A collection system hydraulic model was needed to characterize existing conditions, operations, and performance, and to evaluate cost-effective solutions to mitigate CSO's in the Town to the CSO Master Plan's level of control. The model was developed and calibrated with data from pump stations, the WWTFs, and flow meters installed in the collection system. A Jacobs 'autocalibration' tool enabled a cost-efficient and expedited calibration to the nine flow meters and other data points. Once calibrated, the model was used to evaluate proposed improvements to the collection system needed to eliminate SSOs and sewer backups, and reduce CSO overflows to the CSO Master Plan's level of control. The following goals were established for the analysis: 1.Eliminate CSOs at the West Street PS CSO outfall (Outfall #007) for the 5-year, 24-hour design storm. 2.Elimination of CSOs at the Rodick Street PS outfall (Outfall #006) and Main Pump Station (or Lower Main) outfall (Outfall #004) for the 1-year, 24-hour design storm. 3.Eliminate SSOs at known problem areas in the collection system for up to the 5-year, 24-hour design storm. Results/Benefits: A list of pump station, force main, storage and interceptor improvement projects were conceptualized to increase the collection system's hydraulic capacity and meet the stated assessment goals. The Town had several planned Capital Improvement Projects (CIP) that were included in the alternatives developed; however, prior to the model development, the Town had no way to quantify the potential improvement from these projects. The alternatives were combined in several different combinations to determine the most effective scenarios to achieve the assessment goals. The five most effective scenarios with respect to feasibility and performance were identified and modeled. Each scenario was evaluated with implementing three levels of I&I reduction (i.e., 0%, 25%, and 50%). Conceptual cost estimates for each scenario were developed to further assess the cost-effectiveness of each alternative and its performance towards achieving the assessment goals. This scenario evaluation identified that by optimizing the operation of the West Street PS and CSO Storage Tank project (a $9M project already in design), combined with an upgrade to the Town's Main Street Pump Station (with a combined cost of $4.7M), assessment goals were nearly achieved. The West Street PS project's original design goal was to provide storage for the 5-year, 24-hour event to mitigate CSOs from CSO Outfall #007; the tank was not originally utilized for lower volume storm events and thus the project not maximizing the benefits from the Town's infrastructure investment. By modeling the system using smart, real-time controls, the evaluation showed that the storage tank should be utilized for storage during smaller events, without compromising its goal eliminate CSOs from the West Street CSO Outfall during the 5-year event. The evaluation showed that with these two infrastructure improvement projects, combined with implementation of a 25% I&I reduction program, the Town would not need to complete other CIP projects originally thought to be necessary to meet assessment goals — saving the Town millions of dollars in unnecessary infrastructure improvements. Conclusion: The systemwide conveyance assessment of the collection system is complete and the Town has a plan to achieve CSO mitigation regulatory requirements, as stated in their CSO Master Plan. The West Street PS and CSO Storage Tank Project design is nearing completion and is planned to go out to bid in spring 2024 with construction starting in early summer 2024. With this assessment complete, the Town has the data and information necessary to justify to their ratepayers the benefits and necessity of the ongoing system improvements and planned capital investments into the collection system. The Town also has the data and information necessary to justify the effectiveness of the planned capital improvements to the MEDEP and the information to support completion of the next CSO Master Plan Update which is required to be submitted to ME DEP by March 28, 2027. With the collection system upgrades planned, once constructed, the Town will also have the real-time data needed to verify system improvements are meeting their CSO mitigation goals and the ability to adapt system logic, if necessary, to improve system performance. A truly adaptive solution.