The Western Virginia Water Authority (Authority) is completing a two-phase project at the Roanoke Regional Water Pollution Control Plant (WPCP) to rehabilitate and upgrade the existing anaerobic digestion system and implement a new digester gas conditioning system (DGCS) to produce renewable natural gas (RNG). The RNG will be injected into the local gas utility's (Roanoke Gas Company, RGC) nearby distribution system to generate and sell Renewable Identification Numbers (RINs). Upon its completion, the facility will be the first biogas to pipeline process of its kind in the Commonwealth of Virginia. The first phase of the project includes structural, process mechanical and electrical improvements to five 1.1-MG primary digesters. The digesters are of concrete construction and were originally built in the 1950s & 1970s. Drone technology was used to inspect and assess structural defects within the five digester tanks. Three concrete covers are being replaced with new concrete covers and an elastomeric coating system to improve the capture efficiency of biogas. The second phase of the project would not have been possible without the close collaboration between the Authority and RGC. A feasibility study was conducted to assess overall project economics and gauge RGC's interest in accepting RNG/ partnering on the project. Membrane separation was selected as the preferred technology for carbon dioxide removal and RGC provided minimum RNG quality specifications (higher heating value, carbon dioxide, oxygen, hydrogen sulfide, moisture, pressure, etc.) required for injection. A life cycle cost evaluation considered two methods of tail gas treatment and several DGCS manufacturers. Tail gas treatment methods included a regenerative thermal oxidizer (RTO) and a third membrane pass to reduce methane discharge to less than 1.5%. Although the third membrane unit carried a greater capital cost, it had a similar life cycle cost due to additional methane recovery and RIN revenue (due to greater methane capture). A third membrane pass was selected since it can be provided within the DGCS enclosure, avoiding the need for a separate piece of equipment that must communicate with the DGCS. A sensitivity analysis was performed to assess the risk of variable D-3 RIN prices and operation and maintenance (O&M) costs. As shown in Table 1, this analysis found that the pipeline injection system would generate revenue over a 20-year period if the average RIN value is maintained above $1.35. Once the digester upgrade (phase 1) is complete, average biogas production is estimated to range from 300,000 & 320,000 cubic feet per day. The DGCS manufacturer was pre-selected concurrently with the final design phase through an evaluated bidding process. Technical and cost proposals were solicited from three DGCS manufacturers. The manufacturers were scored based on: 1. Quality of Proposal 2. Cost 3. Experience and Qualifications 4. Warranty 5. Service Capability 6. Installed Horsepower References from a total of six operating utilities were contacted to support the Experience and Qualifications scoring. The overall highest ranked manufacturer was selected unanimously and was not the lowest cost. The selected manufacturer worked closely with the project team to create shop drawings in conjunction with final design efforts. The Authority and RGC came to an agreement that RGC would own and operate the DGCS and interconnect facility, and purchase raw biogas from the Authority. Although the Authority initiated the DGCS equipment procurement, RGC purchased the equipment shortly after the change in ownership was confirmed. Once all operating and maintenance expenses and RIN revenues are quantified after the first year of operation, the Authority and RGC will mutually agree to a division of profits. RGC continues to evaluate the following options for selling RINs; 1) selling RNG directly to an end user capable of utilizing the gas for transportation fuel, 2) solicit a third-party carbon broker to sell the RNG and environmental attributes to generate, document, register, market and monetize RINs, 3) sell the RNG themselves and manage the offtake agreements, tariffs, provisions and all other accounting aspects. The project is on schedule to start injecting RNG into the natural gas grid in Fall 2022. This paper will present the life cycle cost evaluation, provide insights on the design-concurrent best value manufacturer selection, and discuss the arrangement between the Authority and RGC to share in project costs and revenues.

Using the right tools for the job will help planners, reviewers, and regulators make informed decisions to create more resilient, sustainable, and value-driven stormwater solutions. The stormwater systems and watersheds of urbanized areas are more interconnected than most people understand. Urban stormwater systems direct flow through underground systems that often differ from the natural drainage paths. Stormwater flows on the surface when these systems surcharge, following the natural surface flow paths and sometimes contributing to adjacent stormwater systems. In addition, urbanization can lead to low areas that can only be drained by enclosed systems that were not designed to accommodate them. These single outlet systems have no redundant flow paths and frequently lead to deep flooding, impacting homes, businesses, and vehicles. More sophisticated tools, such as 2-dimensional (2D) modeling, allow for visualization of where overland flow paths occur. These visual outputs can help inform stakeholders' decisions on critical infrastructure, emergency planning, and future stormwater system improvements. In addition to understanding surface flow in urban areas, many standard hydrology and hydraulic methodologies, which are sometimes antiquated, can cause the overdesign of stormwater systems. Overdesign can be especially detrimental in older urban areas where urbanization has already overburdened the stormwater system. Following a more realistic and 'right-sized' design approach will help reduce the unintended consequences of overdesigning in these areas. These practical design approaches can also use more sophisticated hydrologic and hydraulic analyses to understand the problem clearly, providing the opportunity to create projects that provide the most value and community benefit. One aspect of this right-sized approach is understanding the 'knee' of the cost-benefit curve. This curve is created using the flood reduction cost for various rainfall events and plotting them against their probability of occurrence. This curve provides the point of diminishing returns for project value versus increasing cost, helping stakeholders and planners understand the current level of service for the stormwater system and how much benefit is realistically achievable. Many communities still use antiquated policies, criteria, and guidance that work in contradiction to creating more resilient and sustainable stormwater systems. Updating local policy and stormwater criteria may be necessary to accommodate these more resilient, sustainable, and value-driven design approaches. Another approach to more resilient stormwater criteria is to break up the watershed into areas with three goals: detention/retention, conveyance, and floodplain regulation. Detention/retention areas are typically farthest upstream and outside the influence of the existing stormwater systems. Conveyance areas generally are in the middle reaches of the watershed and are primarily influenced by the capacity of the stormwater system to convey flow. The floodplain regulation areas are at the downstream end of the watershed and are associated with FEMA regulatory streams. 2D modeling and other tools can be used to define these areas and allow for criteria and policies to be developed to address how these areas influence the flood risk in the watershed. Attendees will be presented with a summary of how antiquated design approaches can lead to overdesigned stormwater systems, how more sophisticated tools can provide more insight and understanding of stormwater challenges, and how they can be used to develop more practical solutions. Through example projects, attendees will have the opportunity to learn about how more sophisticated tools can be used to assess urban drainage challenges and create more resilient, sustainable, and value-driven solutions.

Background Houston's wastewater system is one of the largest and complex in the nation with 39 treatment plants, 381 lift stations, and over 5,900 miles of pipes. On April 1, 2021, a consent decree (CD) between the City of Houston, the United States Environmental Protection Agency (EPA) and the State of Texas was signed to improve Houston's wastewater system. The City of Houston, as part of its Consent Decree, is tasked with developing an Advanced Infrastructure Analytics Platform (AIAP) which incorporates concepts of one-source data, data dynamism, self-service data, and interactivity to facilitate all functions of a wastewater planning group in a synchronous way. A part of AIAP is the Living Infrastructure Plan (LIP). The Automated Capacity Evaluation (ACE) tool fits into LIP as the main capacity evaluation, and capacity alternative recommendation component using hydraulic models as the bases of recommendations. Problem ACE will assist the City of Houston to make capacity-based decisions on a more continuous, living basis using up-to-date data, and yields quick at-your-fingertips results for decision-makers. The alternatives ACE provides are not exhaustive, nor are they prescriptive in the sense that they provide 'a solution'. ACE simply puts alternatives processed through its limited framework at the fingertips of decision makers in a consistent, efficient, and quick manner. Opportunities The City of Houston has devoted considerable resources to develop Innovyze ICM models for their 39 Service Areas. These databases contain considerable data, including networks and simulation data. Innovyze provides a backdoor to ICM called ICM Exchange which allows a script to interact with the wealth of data in ICM automatically. Combining ICM Exchange with the existing ICM databases allows for complex, automated scripting. The City of Houston had developed logic for capacity evaluation. ACE combined the logic of capacity evaluation, the databases of ICM, and the scripting ability of ICM Exchange. Approach The alternative generating part of ACE revolves around four strategies: Inflow and Infiltration Reduction (IIR), conveyance capacity improvements, offline storage, and inline storage. ACE is heavily dependent on the current network for potential solutions. For instance, a new tunnel alleviating overflows which follows a path unrelated to the current network (perhaps related to existing road alignments) will not be a solution provided by ACE. Instead, ACE determines capacity constraints within the existing network layout, and adjusts parameters within the existing network such as conduit width, head-discharge curves, and pump stage on/off. ACE also creates new assets such as offline storage nodes, and inline storage lines -- these new assets are determined by hydraulic constraints and current network layout, not using data such as road alignments or land ownership, although these may eventually roll into ACE. The four strategies of ACE can be interlinked, optimized, analyzed alone, and compared. Strategies can be viewed in complex series, where output from one strategic process influences the input of another strategic process, or the strategies are performed in parallel where within each process decisions are made between strategies. Some strategies require significant iterations, and for iterative processes each iterative step yields a result. From these results an optimal iterative step can be chosen. The only finalized strategy of ACE today is conveyance. All other strategies remain in development. The framework for sequencing strategies and the majority data processing involved for all strategies is also complete. The conveyance strategy is a complex, iterative decision tree. The outcome of the conveyance improvement strategy isn't one solution, but an array of solutions ranging from no improvements to improvements that meet certain trigger and design criteria. The conveyance improvement strategy moves towards these success criteria in a step-by-step fashion by upsizing certain pipes -- not all pipes -- by 1 standard diameter each iteration, and by upsizing certain pumps - not all pumps - when needed so that they are not acting as a downstream capacity constraint. The outcome provides two vital, and impactful pieces of information for the given scenario: an analysis of which pumps need upsizing and by how much after upstream capacity constraints are relieved, and which pipes need upsizing. Of course, these outcomes are specific to the success criteria used, and the scenario fed to ACE. A specific example of the Eddington Lift Station Service area will be used to show an example of results achieved by ACE conveyance improvements. Results A specific example of the Eddington Lift Station Service area will be used to show an example of results achieved by ACE conveyance improvements. Eddington is a small area in the Sims Bayou Service area which includes a single pump, and roughly 1100 acres encompassing approximately 60,000 LF of conduits ranging in size from 4' to 36' diameter, and over 250 nodes. Conduits are improved over seven iterative steps, each step yielding larger diameter pipe. The final alternative, which is not necessarily the cost-value optimized solution but is the hydraulically optimal solution based on the trigger and design criteria, requires upsizing of 36,000LF of conduit, or roughly 60% of the total system. This 60% number can be broken down further into two groups -- pipes which were upsized due directly to the success criteria, and conduits upsized to ensure upstream conduit width is less than or equal to downstream conduit width. Indirect upsizing accounts for roughly 25% of the total conduits upsized. Conclusion and Lessons Learned: Among the lessons learned in ACE revolve around the complexity and importance of having one source of data in order to have a real-on-the-ground satisfactory solution that has community context embedded in decision making many datasets need to be utilized. The City of Houston's Advanced Infrastructure Analytics Platform is addressing this need. ACE can provide benefits to utilities of all sizes, and ACE as a process can be applied to any utility regardless of model vendor. This presentation will focus on ACE, methods and processes involved in ACE, benefits of ACE as a decision-making tool, contextualizing ACE within the larger City of Houston AIAP framework, outcomes of the conveyance improvement strategy of ACE, lessons learned, and potential future developments.

Introduction Affinity Laws for pumps and fans are commonly known but why aren't they commonly known for decanter centrifuges? Dewatering performance has a large impact on overall wastewater treatment operations and understanding how modern decanter centrifuge technology has evolved is critical to selecting the correctly sized equipment. The optimized selection of a decanter centrifuge and its performance plays an important role in the cost of returned solids (solids recovery) and the cost of disposal (dryness of solids). The scaling methodology (Affinity Laws for Decanter Centrifuges) of capacity and performance becomes a crucial activity. The inner diameter of the bowl has historically been one of the main criteria for comparing decanter centrifuges. However, this approach has not been sufficiently accurate for the prediction of capacity or performance. The holding volume, geometry, and operating speeds all need to be compared. For this purpose, GEA has developed and validated a theoretical model by performing side-by-side field trials. The validation of the G x Volume affinity law (See Figure 1) demonstrates that G force combined with volume are reliable criteria for the scaling of capacity and performance of decanter centrifuges for dewatering in wastewater treatment plants. Hypotheses 1. Comparing geometrically similar decanter centrifuges with an equivalent volume with a higher G force would result in either a higher cake dryness or a greater capacity. See figure 2 2. Comparing decanters with a different bowl diameter but with the same G volume, the performance and capacity would be the same. See figure 3 Methodology 1. Side-by-side operation with two equivalent bowl diameter decanter centrifuges with different G-volume was performed at WWTP Langenberg, Germany, keeping other parameters such as sludge characteristics, concentration of infeed sludge and solids recovery identical. 2. Side-by-side operation with two different bowl diameter decanter centrifuges with an equivalent G volume was performed at WWTP Oldenburg, Germany, keeping other parameters like sludge characteristics, concentration of infeed sludge and solids recovery identical. 3. In both trials, the services of KBKopp (Dr. Julia Kopp) were utilized to determine the maximum sludge dewaterability. See figure 4 for photos of the test equipment and site Results The research establishes that centrifuges with an equivalent bowl geometry, but having different G volume owing to rotational speeds, will have an equivalent capacity at the same performance level or a different performance at the same capacity. The capacity and performance is directly proportional to the G volume difference, and only indirectly related to the bowl diameter. See figures 5, 6, 7 Implications The study brings forward 'G x Volume' as reliable criteria for scaling and selection of decanter centrifuges in wastewater treatment plant design and also brings a paradigm shift from conventional wisdom of bowl diameter as the comparative driver. The research helps in selection of centrifuges that get higher capacity per square meter space or significant reduction in cost of operation (disposal and polymer consumption) per cubic meter of sludge handled. In either of the cases, 'G x Volume' based selection drives towards optimized scaling for reduction in CO2 footprint and an efficient circular economy. The Future The development and use of Affinity Laws for Decanter Centrifuges is on-going and is expected to result in more economically efficient and environmentally friendly operations.

Purpose: Urban areas located near shorelines and/or tidally influenced riverbanks face a growing climate threat from the combined effects of increasing and more frequent rainfall and elevated tailwater conditions due to sea level rise and/or storm surge, restricting gravity-driven sewer performance during periods when capacity is needed the most. These tailwater conditions pose a challenge to historic sewer systems designed to drain by gravity, and this challenge is further exacerbated when rainfall rates exceed sewer design capacities. This presentation will share a case study on how to build resilience in sewer systems against these threats in a dense, urban environment, providing lessons learned to other communities facing similar challenges. Overview of Master Plan: Lower Manhattan is at the core of New York City's transportation system, economy, and civic life. Yet by the 2040's, Lower Manhattan's shoreline will begin to experience frequent tidal flooding from sea level rise, impacting streets, sidewalks, buildings, and critical infrastructure. In addition to tidal flooding, Lower Manhattan is at risk from more frequent and severe storms, like hurricanes and nor'easters, bringing storm surge and rainfall to this low-lying area. This has been exemplified by the devastating effects of Hurricane Sandy in 2012 and the record rainfall and widespread pluvial-driven flooding from Tropical Storm Henri (2021), remnants of Hurricane Ida (2021), and remnants of Tropical Storm Ophelia (2023). To reduce both acute and chronic flood risk to the neighborhood, NYC Economic Development Corporation worked with an Arcadis-led consultant team to study climate adaptation strategies and develop a Climate Resilience Master Plan. A major challenge of the master plan was how to upgrade and adapt the city's aging, gravity-driven, combined sewer system to mitigate the combined effects of rainfall, sea-level-rise, and storm surge-driven flooding in this future climate. To do so, the use of the sewer system during extreme weather events had to be re-imagined relative to its original design. This challenge was coupled with designing a coastal flood barrier system in a densely urban area, requiring an assessment of both on-land and in-water solutions (i.e., extending the shoreline of Lower Manhattan via land reclamation) to implement a comprehensive flood risk reduction strategy. To develop the Climate Resilience Master Plan, the team first built a 1D-2D hydrologic and hydraulic (H&H) model of the study area. One complexity of the model-build was the necessity to include upstream drainage areas and downstream discharge areas along the interceptor system so that operation of storm surge isolation components could be assessed across neighboring coastal flood protection system projects. After developing the model, the team identified the depth and extents of surface flooding that would occur under a variety of existing and future extreme weather events assuming a coastal flood protection barrier was implemented without upgrading the existing sewer system. The team then worked across multiple city agencies and stakeholders to develop level-of-service goals for the master plan under these future climate events and developed an alternative analysis to identify a suite of proposed drainage solutions that could meet the level-of-service goals under future sea level rise, storm surge, and rainfall conditions. The alternatives were evaluated for performance, constructability, cost, long-term and emergency-use operational requirements (e.g., operating large interceptor gates and/or pump stations during hurricane conditions), and alignment with other design components of this large, multi-disciplinary project. After evaluation, a subset of stormwater management solutions was carried forward for further development in the master plan, including an innovative approach to reverse the flow in a large-diameter existing interceptor sewer during extreme weather events, a large emergency-use combined sewage pump station, sewer conveyance improvements, and a green infrastructure corridor along the proposed extended shoreline. These solutions needed to fit within a multi-level, community-serving waterfront that maintains access for residents, park space, and active ferry terminals. Benefits of Presentation: Benefits of the presentation include the lessons-learned for many coastal and riverine communities that will face similar climate challenges in coming years, and sharing the innovative solutions employed here that may be considered on similar projects. The presentation will highlight the challenges of designing and siting new drainage infrastructure in dense, space-limited neighborhoods, and considerations for how to integrate this new infrastructure in an existing, aging sewer system. It will discuss considerations regarding coordination with stakeholders on adjacent, ongoing coastal resilience projects. Finally, it will share lessons learned and recommendations to other communities facing similar challenges. Status of Completion: The Master Plan was completed and released in December 2021 and is shared with the public at: [https://fidiseaportclimate.nyc]. The team is currently advancing the early design and engineering of the master plan, which will be completed in 2025. The presentation will cover the completed master plan and new components incorporated in the ongoing work. Conclusion: The employed methodology, proposed solutions, and lessons-learned provide an example to address similar issues in urban areas impacted by the combined effects of increasing rainfall and coastal or tidal riverine tailwater conditions throughout the United States. The presentation will explain the challenges with operating combined sewer systems to meet current level-of-service goals under a future climate and then describe the H&H modeling approach to assess flood risk and alternative analysis to identify mitigation strategies to build a more resilient Lower Manhattan.

INTRODUCTION The City of Chattanooga (the City) owns and operates the 870-megaliter per day (ML/d) Moccasin Bend Wastewater Treatment Plant (MBWWTP) that discharges treated effluent to the Tennessee River. Over the last 20 years, the City has been making strategic investments in planning level studies and innovative technologies to engage in the circular economy. Recently, site constraints and a limited capital improvements budget drove the City to investigate how thermal hydrolysis (TH) pre-treatment paired with intensified anaerobic digestion could optimize the capacity of existing assets thus avoiding costly anaerobic digestion (AD) expansion work in the future with potential economic paybacks through resource recovery. A previous investigation of TH+AD versus conventional AD indicated a narrow margin in capital and annual operating costs, however conservative planning criteria resulted in a recommendation to forego TH and expand the existing digester complex. Preliminary calculations suggested more aggressive planning criteria for a TH+AD alternative could result in a more favorable 20-year life cycle cost and opportunity for long-term return on investment through resource recovery. However, limited full-scale proof of such aggressive criteria presented unacceptable risk and required application of uncertainty factors that would again render TH+AD economically unfavorable. Therefore, the City elected to make a small ($500,000) investment in a pilot-scale demonstration study to generate site-specific data and a comprehensive life cycle cost evaluation. The objective of this paper is to discuss how the City used the pilot-scale study to de-risk a conceptual level life cycle cost evaluation and avoid approximately $50,000,000 in capital and operational expenditure over a 20-year planning period. METHODS The City completed a TH+AD pilot study to inform cost-estimating efforts associated with implementation of TH+AD at the MBWWTP. The results of this pilot study were used together with analysis of historical operating data, previous planning efforts, and industry experience to conduct a comprehensive, life cycle cost-based business case evaluation (BCE). The primary components of the BCE included flow and load projections, conceptual design of alternatives, pilot-scale testing to empirically verify the potential benefits to anaerobic digestion and sludge dewaterability, detailed capacity analysis of the existing facilities, and calculation of the 20-year life cycle cost of alternatives. The evaluation proposed and compared three alternatives: Alternative 1: Conventional Anaerobic Digestion Alternative 2: Partial-Plant TH and Intensified Anaerobic Digestion Alternative 3: Full-Plant TH and Intensified Anaerobic Digestion Site-specific operating data derived through the pilot evaluation are summarized in Table 1 and were supplemented with additional vendor testing, literature, and industry experience. These data were used to develop conceptual designs for the three alternatives including major equipment size, type, quantity, configuration, and performance. Table 1: Summary of Pilot-Derived Data Cost estimators developed a Class 5 Opinion of Probable Construction Cost (OPCC) based on the conceptual designs and price information provided by equipment vendors. The Class 5 OPCC included construction costs (direct costs and general costs), taxes, bonds, insurance, and 25 percent construction contingency and is summarized in Table 2. Escalation, estimate contingency (2.5 percent), engineering, and administrative costs are not included in the OPCC but are included in the Total Project Cost Estimate (TPCE) used in the value business case evaluation. Table 2: Capital Cost Estimates Annual O&M costs were estimated assuming 2034 annual average flow conditions (Table 3). Electricity costs were based on the number of duty units in operation at 2034 annual average solids loading conditions. Chemical costs included pre-THP dewatering polymer and biosolids dewatering polymer. Operational and maintenance labor costs were based on experience at other THP facilities and the City's hourly wage rates. Biosolids hauling costs were estimated based on the projected wet tons produced annually and vendor quoted costs for handling Class A and B biosolids. Table 3: Annual Operating Cost Estimates Finally, results were incorporated into a qualitative alternatives assessment to incorporate non-monetary considerations associated with the triple bottom line into the decision-making process. The team worked collaboratively with multiple City stakeholders to evaluate and rank each alternative under 11 criteria (Table 4). Table 4: Qualitative Evaluation Matrix RESULTS 20-year life cycle costs were prepared assuming design and construction of all alternatives occur over four years, beginning in 2020. The cumulative annual life cycle cost of each alternative was calculated (Figure 1). The estimated annual expenditure was similar for each alternative, with TH-based alternatives being slightly less due to significant savings in biosolids hauling costs. Alternative 2 was shown to have the lowest life cycle cost. However, concerns with partial-plant TH were identified early in the evaluation including inability to achieve Class A biosolids. As a result, Alternative 2 was eliminated. Alternative 3 had a lower life cycle-cost than Alternative 1 and a more favorable score in the categorical comparison. Therefore, Alternative 3 was selected as the recommended alternative. Figure 1: Cumulative Life Cycle Cost CONCLUSIONS The City's small investment in a pilot-scale demonstration study resulted in meaningful, site-specific data that increased confidence in planning criteria and life cycle cost estimates that were ultimately used to make important capital planning decisions. As a result, the City anticipates approximately $50M in capital and annual operating cost avoidance over the 20-year planning period. Several additional recommendations were proposed based on findings made throughout the evaluation. Recommendations are summarized in chronological order below. 1. Further de-risk planning and budgeting efforts by conducting a solids sampling campaign confirm or revise the blended sludge assumptions made under this evaluation. 2. Review and update flow and load projections and re-evaluate facility build-out capacity. 3. Progress Alternative 3: Full-Plant TH+AD to Preliminary Design (30 percent). Conduct value engineering, a Class 3 cost estimate, and an alternative delivery method evaluation. 4. Evaluate secondary treatment capacity considering current performance, future performance under projected flows and loads, current and future nutrient regulations, and opportunities to retrofit existing infrastructure for sidestream treatment. 5. Design and construct full-plant THP and intensified anaerobic digestion incorporating findings from recommendations 1 through 4. 6. Design and construct sidestream treatment (likely in conjunction with TH project). 7. Evaluate energy management alternatives in a small study after TH and digester system commissioning. 8. Implement selected energy recovery based on results of evaluation and available funding.

INTRODUCTION AND PURPOSE The Great Lakes Water Authority (GLWA) is Michigan's largest regional wastewater collection and treatment system encompassing eighty-six wholesale customer collection systems across three counties and 944 square miles in southeast Michigan. The regional collection system serves approximately three million people, representing one third of the state's population. GLWA operates the regional collection system and Water Resource Recovery Facility (WRRF) through a lease from the City of Detroit. The leased facilities include 183 miles of trunk sewer, interceptors, and outfalls; 6 pumping stations, 16 in-system storage devices, 8 retention treatment basins and screening and disinfection facilities, the WRRF and associated metering and control facilities. The City of Detroit Water and Sewerage Department (DWSD) owns and maintains the wastewater collection system and water distribution system within the City of Detroit. GLWA Member collection systems include 77 untreated CSOs, several points of SSO during large weather events, 12 CSO retention and treatment facilities, and 14 sanitary retention basins, and an estimated 3,000 MS4 separate stormwater outfalls. A high degree of structural optimization has already been achieved through local water quality improvement initiatives, NPDES permit compliance, and operating protocols developed over more than 30 years of combined sewer overflow (CSO) control. The Regional Operating Plan (ROP) is intended to further optimize operations by analyzing the detailed system response to storm events, including expanded sharing of real time SCADA data. This presentation describes the development and integration of GLWA's regional collection system model with a GIS-based digital twin platform that integrates near real time data from SCADA, radar rainfall, and overflow reports with the collection system model. The digital twin is a key element of GLWA's ROP, which was developed to optimize wet weather operational performance across six major wastewater utilities that are wholesale customers to GLWA's regional collection system. This close integration of model and data in the digital twin allows for rapid post-event monitoring and near-real-time analysis of collection system performance during wet weather, facilitating continuous optimization of wet weather operations by GLWA and its Members. BUILDING THE REGIONAL WASTEWATER COLLECTION SYSTEM MODEL AND THE DIGITAL TWIN GLWA developed a new Regional Wastewater Collection System model using EPA's Stormwater Management Model (SWMM) as part of its Wastewater Master Plan project from 2017 to 2020. The collection system model consists of over 4,400 individual model subcatchments and 16,000 pipes covering the entire GLWA service area, including detailed operating rules to represent dry and wet weather operations at key facilities. The model was calibrated to metering data to meet the calibration metrics issued by the Chartered Institution of Water and Environmental Management (CIWEM) Code of Practice for the Hydraulic Modelling of Urban Drainage Systems. The digital twin builds upon the collection system model, and integrates the following elements (Figure 1): - The calibrated and validated collection system model - Gage-adjusted radar rainfall data from Vieux and Associates at a 1-kilometer grid cell resolution adjusted to 36 regional rain gages. The radar rainfall data are sent daily at 5-minute increments and applied to all 4,400 model subcatchments - 540 individual measurement points at 5-minute intervals sent daily from GLWA's Ovation SCADA system. These points represent river stage, pump and gate operating records, and flow metering. - Post Event Reports generated after significant storms to document combined sewer overflow events. The digital twin was built in PipeCAST, a web-based GIS platform that integrates monitoring data and modeling results to facilitate decision-making and post-event analysis in near real time. Its foundation is built upon the concept of the digital twin, which is a virtual copy of the collection system that is used to generate real-time simulations from current weather and precipitation conditions (Figure 2). The PipeCAST system automatically receives data from the radar rainfall grid, climate data from NOAA, and SCADA data through a secure application programming interface (API) connection and runs the collection system model for the previous day. The direct connection to SCADA allows the model to simulate dynamic backwater conditions at each CSO outfall and actual pump station operations. The PipeCAST interface provides a GIS-based visualization of metered and modeled flow, depth, and velocity in the collection system, rainfall statistics, and a dashboard that shows key statistics related to overflow frequency and duration. The GIS-based interface can also provide high-level statistics on system performance, such as pipe capacity during wet weather (Figure 3), which can be used to identify potential locations for additional in-system storage. Since the digital twin integrates data and runs the collection system model daily, GLWA can quickly review system performance after storm events and compare model simulations to observed measurements to use as the basis for ongoing model and measurement improvements. APPLYING THE DIGITAL TWIN GLWA is using the PipeCAST digital twin for post-event analyses, where users review wet weather performance relative to the ROP goals. As an example, GLWA used PipeCAST to evaluate system performance for a recent wet weather event in July 2020. This event was 2.05 inches in 10 hours at the Wayne County Metropolitan Airport, and was approximately a 2-year, 1-hour event. The rainfall was most intense north of Detroit, as seen in the color-coded radar rainfall map in Figure 4. GLWA used the digital twin to evaluate how in-system storage and CSO control facilities conveyed flows from the Conant-Mt. Elliott Sewer that serves Oakland County and central Detroit (Figure 5). Flow and system performance were monitored during this event using the digital twin by reviewing incoming flow from Oakland County, in system storage, and performance at the Leib Screening and Disinfection Facility (SDF) (Figure 6). During this event, the incoming flow from meter SE-S-1, (blue line) peaked at approximately 245 cfs, followed by a short-duration peak from the local combined sewer drainage system in the DWSD collection system (meter DT-S-11, orange line). The in-system storage device, controlled by an inflatable dam, was activated, and no discharge occurred from the Leib SDF facility. Based on the review of data using the PipeCAST digital twin, GLWA was able to conclude that the system performed well during this large event, maximizing in-system storage, and minimizing discharges to the Detroit River. CONCLUSIONS GLWA developed a digital twin of its regional collection system to enable post-event analysis to support the ROP. The digital twin was developed using PipeCAST, a GIS-based tool that integrates metering data and modeling data into a platform that allows for rapid review and assessment of system performance during wet weather. The digital twin is being used to complete post-event analyses following significant precipitation events to further optimize wet weather operations, reducing CSO to receiving waters and maximizing secondary treatment at the WRRF.

Key Takeaway: The implementation of a tunnel program is an evolving process that must continually adjust to changing conditions. Learning Objective: Optimizing ALCOSAN's CSO control approach considered multiple issues and challenges associated with the deep tunnel system proposed as an integral part of ALCOSAN's Clean Water Plan. A key consideration was the determination of the cost effectiveness of the primary components given the necessary flow capture to meet the water quality objectives. Additional issues and challenges included flow management for capturing, storing, and conveying CSO to the tunnel and then through the tunnel system to the Woods Run Wastewater Treatment Plant (WWTP) for treatment. The tunnel system and the WWTP are connected at a new dewatering pump station must be hydraulically matched for various flow scenarios. Horizontal and vertical alignments of the tunnel and near surface facilities were optimized considering economic, community, property, and subsurface conditions. This paper will summarize the activities started under ALCOSAN's Preliminary Planning project and continuing through design to optimize these factors in preparation for the implementation of their CSO tunnel control system. Abstract: Background The Allegheny County Sanitary Authority (ALCOSAN) servicing the greater Pittsburgh area has a mandate to control combined sewer overflows (CSO) along its three rivers (Ohio, Allegheny and Monongahela) utilizing a network of storage tunnels, collection system improvements, and expansion of wet weather treatment capacity at their Woods Run WWTP as illustrated in Figure 1. ALCOSAN completed a Preliminary Planning project that optimized and further defined the tunnel system to a 20% design level in a basis of design report (BODR) provided to the regulatory agencies on October 1, 2020. The tunnel network includes three tunnel stretches: the Ohio River Tunnel (ORT), the Allegheny River Tunnel (ART), and the Monongahela River Tunnel (MRT). The ART and MRT connect to the ORT which extends to the Woods Run WWTP. The tunnels utilize dynamic storage via a 120 MGD dewatering pump station that will pump during and after wet weather events thus reducing the overall storage needs of the tunnel network. ALCOSAN continued the advancement of the first leg of the tunnel system through the design of the ORT. During the design of the ORT, the preliminary design was advanced based on further optimizations and updated property acquisition negotiations. Method The effort included evaluating and improving the hydraulic flow management for the diversion structures, consolidation sewers, drop structures, and tunnel facilities. This evaluation considered a range of storm conditions for both a 'typical year' of rainfall as well as a larger collection system design storm. The work also balanced hydraulic flow management with tunneling and construction challenges that need to be addressed in the highly urbanized area surrounding Pittsburgh. The tunnels were evaluated with advanced transient modeling to identify required air management and surge mitigation measures to control the development of geysers. The basis of design included inflow control systems using gated controls on the highest flow sources to mitigate these conditions. During final design, the surge management approach was further refined to simplify the control approaches based on discussions with ALCOSAN operations staff. The preliminary planning effort also evaluated the optimal methods for capturing flows through diversion structures, consolidation sewers, and/or drop structures; ventilation; as well as configuring the tunnel system to address the flow conditions anticipated for both typical year control storm events as well as larger storm events that exceed the combined conveyance and storage capacities. Comparing different strategies for capturing CSO outfalls through diversion and consolidation sewer systems feeding a consolidated drop structure, or direct diversion and drop to the deep tunnels, were conducted at over 20 shaft sites situated mainly along the three rivers in the Pittsburgh area. The BOD layouts of these facilities were further advanced during final design based on updated existing facilities information, property acquisition discussions and discussions with ALCOSAN operations staff. These strategies also assisted in the development of horizontal alignments that considered property constraints as well as community impacts, construction risks, and operational efficiencies for maintenance and tunnel access. During the final design, the horizontal alignment was optimized to minimize the number of required easements and to adjust for near surface facility location modification based on property considerations. Vertical alignments were developed by considering a phased geotechnical exploration program conducted as part of the project. Over 60 borings were performed to assess the overburden and rock conditions along the planned alignments. An additional 60 boring were performed during the final design of the ORT which confirmed the BOD vertical alignment. Close coordination with the dewatering pumping strategies conducted under ALCOSAN's WWTP Program management effort was also required as the sizing of the tunnel is based on a dynamic storage concept. The tunnel will operate with wet weather pumping occurring as the tunnel begins filling during rain events. The plant will ramp up its wet weather treatment capacity to receive flow from both the existing interceptor through the main pump station and the tunnel dewatering pump station. This 'dynamic storage' enabled the tunnel to be sized efficiently by taking advantage of additional wet weather treatment capacity at the plant. Close coordination was continued during the design of both the ORT and the wet weather pump station to confirm the tunnel sizing. Lastly, the program will take advantage of potential flow reductions experienced through adaptive management over the course of the tunnel implementation planned out to 2036. This will include green infrastructure and other stormwater management strategies such as targeted combined sewer separation opportunities being implemented and/or planned in the future by ALCOSAN and their tributary communities. Implementation of this program will be one of the largest capital improvement projects to occur within Allegheny County and the City of Pittsburgh with construction costs estimated to be over $1.2 Billion. The project will result in a reduction of over seven billion gallons of annual CSO discharge to Pittsburgh's famous three rivers.

As metropolitan areas in the United States grow in population, population density and by land communities are challenges with unique and significant new pipeline engineering and construction. Additionally, utilities are challenged by providing reliable and redundant water supplies to expanding populations, increased density with new vertical construction of residential areas and declining population areas in different areas. Thus, the demand for installation of new underground water infrastructure in congested areas has increased the necessity for innovative and economical systems to go underneath and alongside in-place facilities. Trenchless technology, particularly horizontal directional drilling, microtunneling and pipe jacking have become increasingly popular solutions as they minimize disruption of the public and reduce the environmental impact. These facts have guided permitting authorities to gain interest in these methodologies. Permitting often dictates planning, engineering, and construction of underground water pipelines. This is particular for trenchless pipeline installations beneath roads, railways, environmentally sensitive areas, water bodies, urban areas, and existing utilities. Different governing authorities may have unique standards with requirements of pipe diameter, material, and thickness as well as depth of cover. Thus, engineers, owners, manufacturers, and contractors are challenged to develop solutions that are economic, timely and safe. The purpose of this presentation is to highlight trenchless pipeline construction as it is inherently the most challenging and risky activity involved with pipeline projects. Trenchless engineering and construction require operational expertise, utilizes sophisticated and advanced technological equipment, and faces challenging and non-visible geotechnical conditions. Owners, contractors, and engineers are more challenged by trenchless applications as they need to use best judgment and experience to evaluate numerous project risks and costs with sometimes little available information. This presentation will provide a benefit to our industry by discussing all aspects of trenchless construction with respect to feasibility, conceptual design and detailed engineering. It will further discuss construction considerations as follows that are often overlooked by engineers and owners not familiar with the newest applications and implementations of trenchless. We risks associated with these methods and mitigation strategies to reduce overall project risk. Safety risks, for example, include moving parts and turning equipment, uneven ground, potential Injuries, man-entry operations, fatigue, and mental health. Jobsite challenges include availability of water, site access, site constraints, elevation change, underground utilities, site considerations, long crossing distances and dewatering requirements. Economic considerations include supply chain disruptions, skilled labor availability, increased lead times, increased freight costs, unpredictability of imported equipment and material, material price escalation and potential protesting. Environmental considerations include acts of God, extreme heat, cold, dry and wet conditions. Geotechnical considerations include alluvial soils with very low blow-counts, hard rock with high unconfined compressive strength, millennial boulders, manmade and unknown obstacles, corrosivity, abrasively, potential contamination, groundwater level and artesian pressures, ground settlement, differing soil conditions, gravels, cobbles and boulders, hydraulic fracturing, and inadvertent returns. Technology considerations include ability to steer, accuracy limits / line of grade, equipment breakdown, mislead of lasers and insufficient torque. Direct costs include direct labor costs for both engineering, construction and inspection, easement acquisition, scheduling considerations, permitting fees, project contingency, upfront studies including geotechnical investigations and environmental impact studies. Indirect costs include, but are not limited to, traffic control, job site support, insurance, bonding, and potential litigation fees. Social costs are related to road damage and restoration, noise mitigation, loss of business and business effectiveness, vehicular delays, and extended commutes due to traffic control and road shutdowns, and general community impacts to everyday operations. Bottom line there is a lot to consider. Three trenchless installation methodologies are being evaluated for this presentation: Horizontal Directional Drilling (HDD), Microtunneling (MT), and Direct Steerable Pipe Thrusting (DSPT). Each of these options presents benefits and challenges to critical crossings. For the HDD process, a small diameter pilot hole is first created, then the reaming process begins to enlarge the hole for the pull. This method requires the pipe to be installed at the deepest of all trenchless methods to avoid hydraulic fracture of the in-situ soil. For microtunneling, large launching and receiving shafts are required to launch and breakdown microtunnel boring machines (MTBMs). The cutter head is selected according to the face of the tunnel in this case would be a mixed face condition. Slurry will be necessary to maintain the face of the tunnel to avoid unraveling. Direct Steerable Pipe Thrusting (DSPT) is a modified microtunneling methodology that is launched from surface along a path like HDD in geometry. Unlike HDD, the pipeline is thrusted from the entry side and requires limited space on the exit side. These three options will be discussed as unique yet complimentary alternative methodologies for collection system construction. Final methodology selection will be determined by contractor means and methodologies and qualifications, overall pricing and risk profile for the benefit of the overall project program. The takeaway message will address the objective to understand and quantify the risk levels of trenchless crossings project to facilitate, enhance and model risk assessment. The steps to this process includes analysis and identification of the qualitative risk level factors of each trenchless crossing as well as they contribute to overall project scope. Next, we will determine the significant factors that contribute to the risk level prediction and rank these factors using an Analytic Hierarchy Process. Using this information, we will build an assessment based on both known and assumed factors. Finally, we will make a professional recommendation of method based on criteria above.

SUMMARY
Pima County's unique landscape includes climate temperatures ranging from the low 60's in winter months to the 100's during the spring and summer. Vast coverage areas include urban and suburban populations with numerous mountain ranges resulting in large elevation swings. Due to the extensive network of sewer lines and manholes, Pima County experienced high hydrogen sulfide (H2S) amounts throughout their collection system. The Odor Control Conveyance team wanted to monitor problematic sites to validate known issues and discover any unknown issues which could cause potential health hazards to employees and the public; nuisance due to smell; and pipe corrosion/damaged infrastructure, leading to lowered asset life and possible SSO's due to potential pipe/manhole collapse. KEYWORDS: hydrogen sulfide, odors, SSO, smart sewer, smart water, automation, smart city, smart infrastructure, remote sewer monitoring

INTRODUCTION A UNIQUE CLIMATE LANDSCAPE
Pima County Regional Wastewater Reclamation Department (RWRD) serves 280,000 customers across the Tucson area, covering 420 square miles, 5 jurisdictions, and 2 tribal nations. Vast coverage areas include urban and suburban populations with numerous mountain ranges resulting in large elevation swings. RWRD maintains and operates 3,500 miles of sanitary sewer lines, 67,000 manholes and 8,400 public cleanouts. Pima County's unique landscape includes climate temperatures ranging from the low 60's in winter months to the 100's during the spring and summer. During rain events, data collection from sensors provides flow level data alongside 8 rain collection sites. GPS sensor monitoring provides RWRD with not only sanitary sewer system capacity in monitored areas, but also the amount of Inflow & Infiltration (I&I) entering the collection system that ultimately goes towards the Agua Nueva & Tres Rios Treatment Facilities for treatment.

THE CHALLENGE WHAT'S THAT SMELL?
Due to the extensive network of sewer lines and manholes, Pima County experienced high hydrogen sulfide (H2S) amounts throughout their collection system. The Odor Control Conveyance team wanted to monitor problematic sites to validate known issues and discover any unknown issues which could lead to potential health hazards to employees and the public; nuisance due to smell; and pipe corrosion and damaged infrastructure causing lower asset life and a threat to the Sanitary Sewer System environment (i.e. possible SSO's due to potential pipe/manhole collapse). Prior to deploying smart sewer technology, reactive dosage amount performed at Chemical Dosing Units (CDU) were based on odor complaints within odor loggers capturing H2S PPM data for analysis. Both Liquid Phase and Vapor Phase Treatment were used which increased chemical and labor costs and created greater inefficiencies.

THE SOLUTION: SMART SEWER H2S MONITORING TECHNOLOGY
In order to take a more proactive approach, Pima County deployed 44 real-time satellite monitoring H2S units to provide real-time, low-cost hydrogen sulfide (H2S) monitoring at problematic sites across the collection system. Large amounts of data collected from the units allowed Pima County to better understand their system, pinpoint problem areas and fine tune chemical dosage, in turn, optimizing resources to prevent asset degradation. Pima County was then able to integrate H2S data with their asset management system which gave them the ability to monitor CDU dosing changes and, within an hour or two, see the H2S level change based upon the dosing values applied; reduce chemical dosing based on live trend H2S values; and determine the required usage based on CDU tank level volume to not only extend chemical usage, but to also use the chemical more efficiently. With the API integration, approximately 25,000 data points were pulled into the MS Power BI platform for evaluation along with the Asset Management system (Infor IPS). Numerous sensors monitor mid-large size interceptors and other problematic areas and the sensor data capture allows the department to look at the Conveyance system and more efficiently visualize the data through dashboards, analyze collected sensor data and work orders, and use those dynamic measures to understand the collection system status.

THE PROOF: PINPOINTING HOTSPOTS LEADS TO IMMEDIATE ROI
In addition to a better overall understanding of the system, Pima County has been able to quickly identify and address problematic areas, including CDU site dosing, H2S PPM values, and areas where flow monitoring is needed. Smart sewer technology has allowed them to better allocate resources (staff and vehicle travel costs) based on work order evaluations in comparison with unneeded site visits. The County has gained improved visualization of site conditions leading to a more proactive versus reactive decision-making process. The creation of visual baselines and development of KPIs has minimized issues and alleviated known odors. And, the 24/7/365 eyes and ears of the sewer allow real-time evaluation of any changes in the system, making chemical dosing dynamic, thus allowing for reduction in chemical costs and/or allocation of saved chemicals for timeframes when chemical is needed.

This presentation will demonstrate how Goleta Sanitary District (GSD) benefited from having a flexible bioenergy recovery plan and analytical tools to adapt to changing external factors such as funding availability, capital costs, biosolids hauling costs and evolving emission regulations. Attendees will learn the value of revisiting previous decisions when new data becomes available or conditions change and the advantage of having an analysis tool to visualize new outcomes. GSD developed a Biosolids and Energy Strategic Plan (BESP) in 2019 to better capitalize on the energy available from gas produced by their anaerobic digesters at the Goleta Water Resource Recovery Facility (WRRF). The project team used an interactive energy, mass, and financial balance tool (Energy Balance and Analysis Tool - EBAT) to evaluate the benefit from multiple bioenergy recovery alternatives including a combined heat and power (CHP) system, renewable natural gas and sludge drying. Digestion expansion, gas storage and CHP were recommended for the near team. Construction of a biosolids dryer was recommended for solids management about 10 years after digestion expansion to reduce hauling costs and produce a Class A product. GSD began preliminary design work in 2020 to implement the recommendations from the strategic plan. The design included a CHP system with a 450kW digester gas fueled engine generator, digester gas treatment, emissions controls to meet the regional emission limit rules, and a gas storage sphere to provide a consistent gas supply and operational flexibility for the CHP engine. The CHP system would initially operate at 75 percent of its rated output, increasing to full output upon implementation of the planned fats, oils, and greases (FOG) co-digestion program. During the preliminary design phases several external factors changed that extended the payback period of the recommended bioenergy recovery strategy (CHP), including: 1.Capital costs of the CHP engine increased 5-10 percent due to the increasing costs of raw materials. 2. Dialog with the Santa Barbara County Air Pollution Control Department (SBCAPCD) indicated that the 450kW engine would fall under the 'Best Achievable Control Technology' (BACT), requiring continuous emissions monitoring system (CEMS) and a higher level of emission reduction equipment which would increase operating costs. 3. Biosolids disposal and hauling costs increased at a higher rate than expected and could justify expediting the sludge dryer installation. As these conditions evolved, the EBAT model was used to re-examine the long-term bioenergy recovery strategy to determine if an alternative strategy would provide a higher level of value. The team tested many different energy scenarios simultaneously. Scenarios were various combinations of one 450 kW engine generator, one or two 160 kW engine generators, SCR and CMS, and funding received from the Self Generation Incentive Program (SGIP). GSD and the design team discussed the risks and benefits of moving forward with a larger system compared to a smaller system such as availability of grants to fund the project, capital at risk, disruption to operations during construction and adaptability to capitalize on future plant modifications such as co-digestion. As demonstrated in Figure 1, the analysis found that the 160kW CHP system provided a shorter payback period than the 450kW system (13 years vs 22 years) primarily due to the lower capital costs per kW, which was achieved by removing the need for digester gas storage and the continuous emissions monitoring system. While the smaller CHP system would not use all the digester gas produced, the addition of a thermal dryer in the near term (at about 5 years) could provide a means to beneficially utilize the digester gas volume that exceeds the CHP capacity. To test this idea, the team again returned to the EBAT model, incorporating the dryer into the financial and energy balance calculations. The adjustable inputs within the model such as dryer uptime, dryer installation year, FOG co-digestion volume and revenue from FOG tipping fees were varied to understand the individual and cumulative impact on the financial outcome of installing a dryer in the near term. GSD used the interactive, Power-BI based dashboard to experiment independently with CHP sizes, dryer installation years and capital cost reductions from funding opportunities. Figure 2 is a screen shot of the EBAT dashboard. Ultimately, the EBAT model guided GSD to select the smaller CHP system as the bioenergy recovery strategy that provides them higher value with less capital risk. The installation year for a thermal dryer is still under evaluation. This case study illustrates the importance of continuously evaluating and comparing different bioenergy alternatives as conditions such as capital costs, emission regulations, hauling costs, market conditions and other variables evolve during the development of a bioenergy recovery project. The development of a flexible long term bioenergy recovery plan as well as an interactive bioenergy recovery analytical tool provided GSD a means to easily navigate changing conditions and ensure the optimal solution in implemented.

PURPOSE
The presentation will provide an overview of the City of Raleigh's Public Utilities Department, Raleigh Water (Raleigh Water) complex collection system odor and corrosion challenges, current approach to treating and handling odor and corrosion, and how modeling was used to evaluate hotspots and optimize treatment. The presentation will benefit the industry by providing integrated approaches to collection system odor and corrosion control assessment, design criteria, planning, and detailed treatment solutions through advanced sewer modeling.

PROBLEM STATEMENT
Raleigh Water is grappling with a complex and rapidly growing collection system with interceptors of varying age and materials, both concrete and inert. Due to the complexity and frequent changes, the system has areas at high risk of high hydrogen sulfide, potential odor nuisance, and corrosion. Raleigh Water maintains an active odor control program with the goal of addressing elevated and consistent odors within the wastewater collection system. The odor control program includes a liquid chemical feed program in which different odor control chemicals (ferrous sulfate, hydrogen peroxide, and calcium nitrate) are added to the wastewater at different strategic points within the collection system to reduce and/or suppress the formation of hydrogen sulfide. Routine monitoring of liquid and gaseous hydrogen sulfide levels is conducted to assess performance at the different dosage locations and to identify any needed adjustment to chemical feed rates. In addition to the chemical dosage program, Raleigh Water also has vapor phase odor treatment systems at several of its regional pump stations to treat the odorous air collected at the pump station. Raleigh Water's strives to build a programmatic system approach for odor and corrosion. Although the Raleigh Water has an expansive chemical dosing system in place that has had success, there are still gaps and areas in need of improvement. Raleigh Water recognizes these gaps and has a goal to optimize their system both for treatment and cost efficiency, while also minimizing elevated and consistent odors system wide.

BACKGROUND AND METHODOLOGY
Raleigh Water operates a collection system that spans over 2,500 miles of pipe, both gravity and forcemain, and conveys wastewater to one of three resource recovery facilities. Figure 1 shows Raleigh Water's collection system, locations of pump stations, dosing stations, and resource recovery facilities. The odor control treatment program is comprised of liquid treatment at more than 20 chemical dosing stations (varying chemical usage) and several vapor phase systems throughout the collection system. The chemical dosing stations throughout the collection system treat the system with different chemicals depending on the location. Calcium nitrate, iron, and peroxide are used throughout the system. In 2017, Raleigh Water completed an odor and corrosion control master plan that evaluated the ongoing treatment program for areas of improvement and potential areas in need of treatment. This was completed through extensive sampling, both liquid and gas phase, and collection system modeling. In 2022, HDR, The WATS Guys, and Raleigh Water worked together to build upon the findings from the previous master plan and assess Raleigh Water's collection system for odor and corrosion control using the Wastewater Aerobic/Anaerobic Transformation in Sewers (Mega-WATS) model. The Mega-WATS model was used for the project because it analyzes and solves complex in-sewer transformations including microbial-induced concrete corrosion, odor formation, and potential for nuisance risk caused by hydrogen sulfide air emissions from pressurized sections of the sewer. Additionally, the model can predict anticipated effects and results of utilizing hydrogen sulfide control strategies, both liquid phase and vapor phase throughout a collection system. The model was used as a key tool in an integrated master planning effort that began in January 2022 and will be completed in December 2022, providing integrated approaches to collection system odor and corrosion control assessment, design criteria, planning, and detailed treatment solutions through advanced sewer modeling. The analysis was done using two modeling scenarios:
1. 2022 average weather and flow conditions
2. 2025 projected average weather and flow conditions

The 2022 model was calibrated using 2015 sampling data as well as updated sampling data completed in June 2022. The model input parameters incorporated existing chemical dosing and vapor phase treatment information to represent field conditions and predict the level of hydrogen sulfide control within the system. The 2022 model findings were evaluated for corrosion risk and areas with high concentrations of hydrogen sulfide in comparison with known odor complaint locations.

RESULTS AND FINDINGS
The 2022 model results were used to determine odor and corrosion hotspots throughout the entire collection system. These hotspots were detected by assessing areas with model predicted hydrogen sulfide presence, known odor complaints, and/or model predicted corrosion. Plots similar to Figure 2 were used to define the hotspot areas and prioritize them based on parameters such as: hydrogen sulfide presence, odor complaints in the area, known high risk asset, high predicted corrosion rate, and known planned monitoring or replacement. The presentation will provide a more detailed assessment of the hotspots and how they were evaluated and prioritized from the modeling results. The 2022 odor and corrosion hotspots were used to develop over ten capital improvements solutions as well as potential operational changes. The developed solutions were primarily related to adding chemical dosing sites in areas with hydrogen sulfide hotspots that were not already being treated, as well as pilot testing different chemicals and combinations of chemicals along flow paths to assess for improved and optimized treatment. One specific flow path evaluated is made up of several oversized forcemains and has an overall detention time of more than 60 hours. The flow path currently has three chemical dosing sites that treat the line with calcium nitrate upstream and iron followed by peroxide downstream. Although his treatment combination has helped mitigate some of the hydrogen sulfide formation, there is still concern for corrosion and odor along the flow path. The project team completed a desktop evaluation on the flow path and found that the addition of a pH adjustment (to a pH between 8-9), such as magnesium hydroxide, upstream of the iron dosing improved the iron's precipitation capabilities with dissolved sulfide. The combination of pH adjustment followed by iron was predicted to be an effective chemical optimization strategy on other flow paths in the system as well. The model also predicted downstream pH with these chemical combinations matched would not adversely impact the resource recovery facility. The team has recommended pilot testing in various locations in the collection system to validate the treatment combination. This presentation will provide the detailed flow path findings, results, evaluation (economic and non-economic benefits), and recommendations that evolved throughout the project. The presentation will provide insight and potential mitigation solutions for other utilities experiencing problematic hydrogen sulfide levels, odorous air, ineffective chemical treatment or corrosion throughout their collection systems.