Silicon Valley Clean Water (SVCW), a water resource recovery agency in California, is nearly complete with its major infrastructure and conveyance upgrade program that used the progressive design-build (PDB) delivery for three interrelated projects valued at $569MM USD. This program, the Regional Environmental Sewer Conveyance Upgrade (RESCU), was implemented to replace SVCW's aging conveyance system and improve preliminary treatment facilities. Since 2016 when the program was initiated, SVCW has been an early adopter of PDB delivery for major wastewater infrastructure and has been focused on learning and sharing lessons learned to improve PDB delivery for the wastewater industry. This paper/presentation is intended to continue the sharing of lessons learned about PDB delivery for water/wastewater infrastructure projects throughout design, construction, startup and commissioning to better educate others who are considering and/or implementing PDB delivery for similar projects and programs. RESCU Overview: SVCW's RESCU program consists of numerous projects; however, the following three large CIP projects are at the heart of the program and account for over $569MM USD of construction cost:

*The Gravity Pipeline Project constructed a new gravity sewer pipeline [approximately 5,200 meters (17,000 linear feet) and 3.4-meter (11-foot) inside diameter], using a tunnel boring machine, that will serve as the main wastewater conveyance system to the treatment plant. Approximate project value is $264MM USD.

*The Front-of-Plant project constructed a new deep influent lift station [approximately 27.5-meter (90-feet) deep, 300,000 m3/d (80 mgd) capacity], located at the terminus of the Gravity Pipeline, and preliminary treatment facilities and connection piping to SVCW's main WRRF. Approximate project value is $169MM USD.

*The Pump Station Improvements Project is rehabilitating three of SVCW's conveyance pumping stations and portions of force main that contribute the flow to Gravity Pipeline. Approximate project value is $136MM USD. See Figure 1: RESCU Overview; Figure 2: Front-of-Plant. RESCU Program Timeline and Highlights: In 2016, SVCW began exploring PDB delivery as a viable approach for these three critical projects due to schedule extensions related to the overall program implementation approach. Like many other agencies, SVCW had to learn a lot about collaborative delivery prior to initiating these projects and talked with other agencies nationwide, attended Design-Build Institute of America (DBIA) conferences, and received guidance from Owner's Advisors. In 2017 through 2019, SVCW worked through a rigorous procurement process to select PDB teams for each of the three projects. The process included a Request-for-Qualifications (RFQ) stage, qualification interviews, reference checking, short-listing of selected firms, a Request-for-Proposals (RFP) stage, a proposal process, additional proposal interviews, confidential meetings and reference site visits to previous projects. From 2019 through present, the PDB teams have been working through individual project designs (BODR, 30%, 60%), final cost negotiation, and construction processes, but were coordinated as a program. Because the same PDB team was selected for both the FoP and PSI project, coordination was simpler between those projects. When the COVID pandemic began, SVCW had already implemented MS Teams for the RESCU Program and quickly to remote meetings with minimal delays. Early work packages were used to accelerate critical elements of work or equipment (such as the tunnel boring machine), which proved to be advantageous just before the pandemic began. As construction progressed through final completion, it became evident that startup of facilities with overlapping responsibility (e.g. Gravity Pipeline and Front-of-Plant) would require careful coordination between PDB teams, which is currently underway. Learning Objectives: The primary learning objectives for the paper are to educate attendees on the 'real life' implementation of PDB process, with particular emphasis on programs that include multiple interrelated projects. Because many agencies still have limited knowledge of collaborative delivery, it is important for our industry to share knowledge from those who have recently implemented this type of project delivery. Although some elements of the RESCU program were presented at WEFTEC 2019, those lessons shared were primarily about procurement and pre-design phases. Now that the program is nearly complete five years later, this paper will focus on lessons learned through the entire PDB process, with particular emphasis on the recent construction and close-out phases (2019-2024) that have not been described yet. Lessons learned will be broken into the following main categories:

*Procurement Process

*PDB team procurement and selection

*Co-location of teams

*Collaborative design processes

*Negotiating lump sum pricing and cost validations

*Benefit of early work packages for construction and critical equipment/material procurement

*Agency involvement during construction (submittals, etc.)

*Equipment selection and procurement using best value

*Design, construction and startup of projects with 'overlapping responsibility'

*Planning for outreach/permitting

*Equipment and/or design issues during startup

*Navigating the COVID pandemic/supply chain issues

Ozone is well known as an effective disinfectant and oxidant and has been operated for drinking water treatment in combination with biofiltration or biologically active carbon filtration for more than 50 years. Its versatility makes ozone/BAC a powerful tool for non-potable and potable water reuse applications. It is frequently applied as major barrier for pathogens and chemicals in carbon-based indirect potable reuse projects, especially for inland applications with limited options for sustainable management of reverse osmosis concentrates. In addition, most recent regulation for California includes ozone/BAC as an important barrier for control of chemicals in direct potable reuse (DPR) projects. In Europe, pilot- and full scale ozonation systems are currently installed in several countries with the aim to mitigate the discharge of chemicals of emerging concern (CECs) into receiving surface waters. Recent regulatory changes are expected to accelerate the implementation within the European Union: In October 2022, the European Commission published a draft of the amended Urban Wastewater Treatment Directive, which for the first time includes requirements for mitigation of organic micropollutants. In addition, EU has defined minimum requirements for agricultural water reuse that came into force on 26th June 2023 and provoked pilot studies testing ozone/BAC also for water reuse applications. This presentation will discuss experiences with ozone/BAF design and operation in Europe and the US, identify key parameters for design and process control, and outline potential concepts for future design. Ozone/BAC for water reuse in the US is designed for simultaneous removal of chemicals and pathogens, often applying ozone to TOC ratios >1 g O3/g TOC. Efficient disinfection (> 6 log inactivation) was confirmed in various spiking tests with bacteriophages at pilot scale. In contrast, ozonation of secondary effluents is designed for CEC removal and recent applications often apply ozone/TOC ratios as low as 0.3 g O3/g TOC. However, even at higher doses around 1 g O3/g TOC only limited inactivation of abundant indicator bacteria was observed in different studies, which often results in the conclusion that disinfection of wastewater by ozone is not effective. While ozone alone is effective for the removal of many contaminants, its combination with post-treatment in BAC filters is typically recommended to remove easy biodegradable oxidation by-products generated during ozonation and thereby lower effluent TOC and adverse effects in downstream processes. Besides, adsorption in BAC filters may serve as additional barrier for CECs if the carbon is regenerated on a regular basis. In our presentation, we will highlight similarities and differences in process design, control and operation in the US and in Europe, discuss potential reasons for deviating results, and outline solutions for an optimized design of ozone-BAC including effective removal of CECs and pathogens as well as the control of by-product formation. The presented results are based on own research (pilot and full-scale studies in Europe and the US) and literature studies including previous work for the WRF project 4832.

The City of Santa Monica (City) is implementing several innovative water supply projects as part of its Sustainable Water Supply Program. The program will leverage alternative water supplies, including stormwater, dry weather urban runoff, concentrate waste stream, and municipal wastewater to provide a diverse, sustainable, and drought-resilient local water supply. Collectively, these alternative water supplies would reduce the City's reliance on imported water supplies and projected to meet over 90% of its water demands through local water resources. The City employed alternative delivery strategies for two, first of its kind projects in its Sustainable Water Supply Program. The first project used a Design-Build-Operate (DBO) delivery model for the City's $96 million potable reuse facility that features the first membrane bioreactor and cartridge filter to receive log reduction values for pathogen removal in potable reuse applications in California, first stormwater harvesting and direct injection project in California, and a completely underground facility at the City's Civic Center to minimize impacts to the community. The second project used a Progressive Design-Build (PDB) delivery to implement the first Flow Reversal Reverse Osmosis (FRRO) system in the United States that will achieve a recovery of 90% or greater. The PDB and DBO delivery method provided a collaborative environment where the City (owner), engineering designer, construction contractor, and operation team partnered together from day one of design through construction completion and transition to operations to tackle key project challenges together. The key project challenges included: deep excavation for an underground potable reuse facility located at the City's Civic Center (adjacent to a Court House, Child Learning Center, and Historic Bel Mar Park), balancing project risk and cost associated with new technology applications (e.g., MBR pathogen removal credits changed during project implementation and no previous full-scale performance track record for FRRO), addressing project funding and supply chain impacts due to the Covid-19 pandemic, and managing regulatory engagement through a progressive design process. The key advantages with using a PDB/DBO delivery method include pricing flexibility (e.g., adjust project scope to meet project budget), flexibility with equipment selection to meet operation preferences, identification of project risks and associated cost to mitigate risk up front, single point of contact, and performance guarantee for project delivery. As alternative delivery methods are still relatively new to the water/wastewater industry, several lessons learned were gained during delivery of the two projects. The lessons learned that will be covered in the presentation include: 1) Procurement of PDB/DBO team — setting project expectations up front and incorporating indicative cost estimate to qualification based selection, 2) Preconstruction phase — partnering early and often, proper QA/QC trumps project schedule, and negotiating a fair performance guarantee and guaranteed maximum price, 3) Construction phase — undefined project scope/condition resolution, and continued regulatory engagement as only 60% design was completed to begin construction. The presentation will summarize the owner/utility perspective of advantages and lessons learned during each phase of the PDB/DBO delivery process for two alternative water supply projects.

BACKGROUND The Ann Arbor WRRF is a 29.5 MGD advanced secondary treatment wastewater facility owned and operated by the City of Ann Arbor, MI. The liquids treatment includes headworks, primary clarification, enhanced biological phosphorus removal (EBPR) , nitrification, final clarification, granular media filtration, and UV disinfection prior to discharge to the Huron River. The solids treatment has been dependent upon the ability to land apply the biosolids for nearly half of the year. During this period, primary sludge (PS) was thickened using gravity thickeners and waste activated sludge (WAS) was thickened by a gravity belt thickener (GBT). Together thickened PS (TPS) and thickened WAS (TWAS) were combined and the biosolids were lime stabilized prior to hauling to local fields. During the rest of the year, when land application was not possible, PS and TWAS were combined in holding tanks before being dewatered by centrifuges. Centrate from the centrifuges was returned to the plant influent, and the dewatered biosolids were hauled to a landfill for disposal. Combining PS and TWAS without the addition of lime, caused phosphate removed by the EBPR process to release into solution and concentrate in the dewatering centrate. For these months, this returned phosphate load reduced the efficiency of the EBPR process, and ultimately increased the effluent Total Phosphorus (TP) concentrations. Ann Arbor is facing challenges associated with increasingly stringent National Pollutant Discharge Elimination System (NPDES) permit limits for effluent phosphorus, with May to December effluent loadings limits reduced from 200 to 50 - 60 lbs total phosphorus (TP)/d. In addition, land application has become more difficult (i.e., farm field availability, transportation issues) causing Ann Arbor to dewater and landfill solids year-round until a longer term biosolids management strategy is developed. To consistently meet the new NPDES permit limits for phosphorus, the City of Ann Arbor engaged a team of consulting engineers to study options for treatment of the high phosphorus centrate side stream resulting from centrifuge dewatering of WRRF sludge. METHODOLOGY The first task in this study was to develop a whole plant process model, which was used to understand the impacts of centrate phosphate loading and evaluate the efficacy of possible mitigation approaches. The project team then identified four alternatives to be considered for mitigation of centrate phosphate loading concerns: 1.Segregated and aerated storage of WAS to prevent phosphorus release. 2.Lime addition to sludge holding tanks to precipitate phosphorus prior to dewatering. 3.Phosphate recovery from the dewatering centrate. 4.Chemically enhanced primary treatment (CEPT) to minimize secondary phosphorus loading. The alternatives were evaluated based on:

*Ability to meet the NPDES limit for TP loading

*Capital and operating costs

*Ease of implementation and operation

*Secondary impacts to plant processes, such as EBPR Following evaluation, bench scale testing was performed for preferred alternatives to validate modeling results and examine operational feasibility. This resulted in one preferred alternative being implemented and optimized at full scale. FINDINGS Simulation results from the whole plant model (Figure 1) demonstrate Alternatives 1, 2 and 4 show the most promise in meeting the strictest year-round final effluent TP load (50 lb/d). Cost analysis, however, showed that the chemical demand associated with Alternative 4 would add nearly $2 million in annual operating cost for Ann Arbor, whereas Alternatives 1 and 2 could be implemented with the fewest operational and infrastructure changes. These alternatives also presented no negative impacts on other plant operations (e.g. EBPR). Benchtop testing for Alternative 1 (Figure 2) demonstrated that it is unlikely that aged PS and aerated TWAS could be mixed for more than a few minutes without releasing more than 20% of the stored phosphate into the centrate stream. Testing observations also identified potential full-scale difficulties with aerating TWAS. Testing for Alternative 2 (Figure 3) predicted a lime dosing rate of 2.3% (18% lime slurry) would provide 90% PO4-P removal in the centrate. Based on this analysis, Alternative 2 — Lime addition to sludge holding tanks, was implemented at the full scale using existing assets in 2023, one year ahead of permit limit reductions taking effect. The plant has met their new NPDES limits (Figure 4) and has been able to optimize the lime dosing operation. Since the initial lime dosing rate of 2.3% was exceeding the targets of 90% PO4-P removal in the centrate (Figure 5), systematic reductions in dosing rate to 1.6% have been completed, resulting in a final sidestream PO4-P removal cost of less than $0.25/lb TP. Under the lower dosing rates, targeted PO4-P removal and daily plant effluent TP limits are still being met on an average basis, however, there is increased variability in daily centrate PO4-P removal rates. This variability has been linked to the final centrate pH, which is thought to be primarily influenced by pre-liming sludge age. The City and its team of consulting engineers is currently investigating and optimizing the sludge holding and lime dosing strategy to reduce this variability. Findings from this optimization will also be included in the final paper.

Introduction: Ultraviolet LED technologies have progressed to the point where full-scale implementation is now on the horizon. The work outlined in this study is part of WRF project 5173 which investigates the feasibility of UV LEDs at different magnitudes of flow and water qualities. A 280nm, 100 GPM, closed-channel UV LED unit was installed in a wastewater facility in Nova Scotia, Canada to compare to a conventional open-channel UV disinfection system. This project represents the first ever installation of UV LEDs for wastewater disinfection at this scale and provides foundational data for understanding how UV LEDs scale as a technology. In addition, the practical experience gained during the installation process of this technology is valuable to consultants and utilities who may be considering the use of UV LEDs in the future. Project Background: Data was collected over a 4-month period before the installation of the full-scale UV LED system using the UV auditing approach. The UV auditing approach has been developed by Dalhousie University and provides an understanding of the delivered fluence for full-scale UV disinfection by leveraging bench-scale inactivation curves (Rauch et al., 2022). This approach has successfully demonstrated that UV LEDs can outperform conventional, mercury-based 254nm disinfection for some wastewater matrices (MacIsaac et al., 2023). UV auditing is also useful for utilities in understanding how LEDs will perform when considering mercury-free disinfection technologies. The LED reactor used for this work (shown in Figure 1) was manufactured by AquiSense Technologies and is a closed channel design with a 100 gallon per minute (GPM) capacity and was conducted over the Fall of 2023. The flow capacity of the LED unit represents approximately 10% of the average daily flow of the wastewater facility that it has been installed at. This installation marks the largest commissioning of a UV LED wastewater disinfection reactor anywhere in the world. Pre-installation data is shown in Figure 2 and was collected during the Summer of 2023. The average UV transmittance measured at the facility during this sampling period was 53% with an average power consumption of 35 KW. The disinfection results indicate that 280nm UV LEDs performed comparably to conventional 254nm low-pressure system and can provide sufficient pathogen inactivation when used at the full-scale. Additional Project Phases: The second phase of this work involves stress testing the UV LED reactor to define the range of performance in terms of power output, flow rate and UV transmittance. This work was conducted over a 4-week period in early 2024 and involved operating the reactor at a flow rate of 100 and 200 GPM, as well as power outputs ranging from 50-100%, and variable UVT during the sampling period. The final phase of this work involves the comparison between the UV LED reactor with the conventional, open channel, low-pressure UV system that is already installed at the facility. This work covers a 6-month period with twice weekly sampling of the inlet and outlet of both treatment trains. A scale analysis concludes this work by collecting samples of internal surfaces at the end of the six-month sampling period. This work identifies the differences in fouling mechanisms between each of the UV light sources. UV LEDs do not generate heat on the emitting side of the light source and therefore, are not expected to form inorganic scales in the same way that conventional mercury lamps do. This work provides foundational information for both consultants and utilities when considering approaches for testing the feasibility of using UV LEDs in wastewater facilities. UV LEDs have shown to be comparable in performance to conventional systems while avoiding several of the environmental, human health, and safety issues related to mercury-based UV disinfection. In closing, the tasks conducted in this work help achieve the goals in understanding UV LED implementation as defined in WRF 5173.

Objectives Hydrocyclones can intensify activated sludge processes by retaining larger, faster settling flocs and eliminating smaller, slower settling flocs. This can result in lower sludge volume indices (SVIs), higher mixed liquor solids concentrations, higher solids retention time (SRT), and modified mixed-liquor microbial community structures (Roche et al., 2021; Regmi et al., 2022; Li et al., 2020). While it is clear that hydrocyclones improve SVIs, what factors impact separation, and how separation impacts microbial communities, is less obvious. For example, does the relative abundance of heterotrophs, AOB/NOB, and PAOs determine whether a floc is retained in the hydrocyclone underflow? What is more important for floc retention: floc density, size, or shape? Do hydrocyclones affect protozoa? Such information could help program hydrocyclones to promote a desired treatment objective. In order to answer the above questions, we are using dynamic floc imaging, molecular tools, activity test, and floc density analyses to explore the effect of hydrocyclones at a full-scale wastewater treatment plant. We have completed four sampling events and expect to have four more by the time of the conference. This abstract includes our ongoing results. We expect to have full results in time for WEFTEC. Methodology Samples were collected from a full-scale municipal wastewater treatment plant in the Midwest region of the US. The plant was configured for EBPR and implemented a densified activated sludge (DAS) process using hydrocyclones in November of 2022. Starting in May 2023, sampling campaigns for floc analysis were carried out approximately every two months. Four samples have been collected and analyzed at the time of this abstract submission. Sampling included hydrocyclone influent, overflow, and underflow, and MLSS. Floc characterizations were carried out with an integrated laser diffraction analyzer with synchronous dynamic image analysis, i.e., diffraction and imaging were carried out on a single sample at the same time (Microtrac, Germany). By analyzing thousands of individual flocs in each sample, this provides classical particle size histograms, but also a large range of morphological particle parameters, such as circularity, sphericity, roughness, aspect ratio, roundness, and fractal dimension. Microbial community characterization was carried out by 16S rRNA gene sequencing of VSS from the MLSS, hydrocyclone influent, overflow, and underflow. qPCR and FISH were used to quantify AOB, NOB and PAOs. Findings A plot of SVI30, SVI5, and densification index over time is shown in Figure 1. SVIs decreased, and the densification index increased, over time after implementing the hydrocyclones. Floc size characterizations showed that the 50th percentile area-based diameter (D50) increased progressively from 108 µm (May 2023) to 163 µm (December 2023) (data not shown). Based on floc size histograms (Figure 2):

*Hydrocyclones appeared have little separation effect on the smaller flocs (0 — 50 µm). These were present in similar amounts in both overflow and underflow.

*The impact of hydrocyclones on larger flocs increased with time, i.e., there needed to be more large-sized flocs in the MLSS in order for the hydrocyclones to separate them into the underflow. Based on an analysis of floc circularity (Figure 3).

*Smaller flocs tended to be more circular than larger flocs, both in underflow and overflow

*Larger flocs in the underflow tended to be more circular than similarly sized flocs in the overflow, suggesting that floc morphology can play an important role in retention by hydrocyclones.

*Differences in circularity between underflow and overflow increased progressively over time (data not shown) Sampling sequencing data is available for one sampling date (July 2023). Based on these results, the hydrocyclone underflow had higher abundances of AOB, NOB, and PAOs than the overflow (data not shown). Interestingly, NOB (Nitrospira sp.) were more abundant than AOB. Preliminary qPCR and FISH (Figure 4) results are consistent with the sequencing. FISH is currently being used to differentiate the microbial communities for different floc sizes and shapes. Percoll density separation is also being used to quantify and sequence flocs by density. These results will be included in the final paper and presentation. Significance The results suggest that hydrocyclones separate not only based on floc density, but also size and shape. The role of microbial community is currently being analyzed and will be presented at the conference.

Introduction Nashville Metro Water Services' (MWS) Central Water Reclamation Facility (WRF) has disinfected its treated plant effluent using gaseous chlorine since the facility was originally commissioned in 1958. Sixty-five years later, after 10+ years of planning, design, and construction, a new 350 MGD ultraviolet (UV) disinfection facility is online, and the last 90-ton rail cars were removed from the site. As of January 2024, the new UV facility has been operating as expected for six months, with E.coli values well within permit limits. The new UV facility is one of largest UV disinfection installation in the United States. Planning Driven by its Consent Decree, MWS commissioned the Central WRF Optimization Study (COPT Study) which recommended improvements to cost-effectively and reliably increase the peak wet weather capacity of its largest treatment facility from 220 MGD to 350 MGD via optimization; rather than by adding expensive new process tankage (Yarosz and Taylor, 2015). Figure 1 is an aerial photo of the Central WRF, which is located less than 2 miles from the heart of downtown Nashville. Since the Central WRF's existing gaseous chlorine disinfection system was unable to treat the large increase in capacity and MWS continued to have concerns with transporting, storing, and handling gaseous chemicals, MWS decided to evaluate alternative disinfection technologies as part of the COPT Study. The Central WRF also had two disinfection locations and desired to simplify operations by disinfecting optimized plant secondary effluent flows in a single location. A business case evaluation of multiple disinfection technologies was performed using both cost and non-cost considerations to determine the most beneficial long-term solution for MWS (BC, 2014). Capital costs, 15-year net present values (NPV) and 20-year NPVs were developed Non-cost factors include constructability, operability, reliability, safety, impact to traffic, and impact of potential future regulatory issues. UV disinfection was selected over sodium hypochlorite (bulk and onsite generation), peracetic acid (PAA), ozone. Table 1 includes the final results of this business case evaluation. Design of UV Facility Consistent with the project's goal to utilize existing structures, the design team determined it was feasible to construct the new UV disinfection facility within the footprint of the existing north chlorine contact tanks (CCT), which were designed to facilitate chlorine disinfection of 150 MGD. The following bullets briefly discuss some of the key design considerations. These and many other design considerations will be fully detailed in the full technical paper, if selected. The existing pile foundation of the CCTs was sufficient to support the new UV facility. The addition of concrete was offset by the reduction in water volume. The existing piles could also accommodate an enclosed pre-engineered metal building for shelter. CFD modeling was performed to confirm there was adequate mixing of north and south secondary effluent flows and determine a UV channel configuration that would not require flow straightening baffles as MWS has experienced algae issues with them at another WRF. Figure 2 shows output from the CFD model, which indicated that the flow split was within 2% of ideal at peak flow. There was limited headloss available to fit the UV facility into the Central WRFs hydraulic profile. Piping modifications upstream of the facility were required to reduce headloss. UV equipment O&M features were developed collaboratively in workshops with O&M staff where the engineers could listen, understand, and incorporate MWS' ideas and preferences into the design. The UV facility was designed around Trojan Technologies UVSigna(R) equipment because Trojan was able to propose multiple configurations that fit within the limited footprint of the existing chlorine contact tank structure, whereas several other leading UV manufacturers could not. Tables 2 and 3 include Design Flows and Permit Values and UV System Design Parameters, respectively. Additional discussion and supporting data related to the parameters in these tables will be included in the full technical paper, if selected. Construction Sequencing The UV facility layout and structural design had to facilitate construction sequencing that maintained plant effluent disinfection with flow routed through the structure throughout the duration of construction, except for several 2-to-5-day long shutdowns that generally occurred between different phases of construction. With the assistance of the Construction Manager at Risk (CMAR), a sequencing plan was developed in which the existing CCT structure was converted to the UV facility one half at a time. Figures 3 through 7 illustrate the sequence of construction, which was completed in approximately 3 years. Figures 8 is a photo from inside the UV facility. Status of Project/Significance of the Investigation All phases of this 10+ year long project are complete and the $35 million UV facility has been operating successfully for 6 months. This technical paper will include performance data, O&M experience, and 'if we could do it over again' insight from the Central WRF plant manager and the design engineer. Utilities, consultants, contractors, and others who are preparing to upgrade their water resource recovery facility (WRRF) disinfection systems can greatly benefit from this project's experience.

Summary Publicly owned treatment works (POTWs) frequently use U.S. EPA-published data on nitrification inhibition thresholds to derive local limits for industrial users discharging to their water resource recovery facilities (WRRFs). For many constituents, the range of threshold values can vary by an order of magnitude or more. Many POTWs, lacking more specific information, consequently default to the most conservative guidelines when setting local limits. Clean Water Services (CWS) conducted nitrification rate testing at its WRRFs to identify facility-specific zinc (Zn) and copper (Cu) nitrification inhibition thresholds and translated these data to local limits. The resulting levels were higher than the EPA-published minimum thresholds for both metals while still providing confidence that resulting local limits would be protective of biological nitrogen removal processes at each WRRF. Background Controlling industrial discharges to a POTW is an integral part of the NPDES permit program. In conducting local limits analyses to establish limits for industrial discharges, POTWs consider several factors, including water quality standards, water quality-based NPDES permit effluent limits, biosolids use and disposal, and the potential for inhibition of WRRF biological processes. The most conservative of these values is used to establish the local limit. Limits are often driven by the need to shield the biological nitrification process from inhibition. EPA has published nitrification inhibition threshold values for a variety of substances in its Local Limits Development Guidance (EPA, 2004). For many substances, a wide range of possible inhibition levels have been identified. Because the data are decades old and studies are not well documented, there is limited confidence that even the most conservative thresholds would be protective of biological treatment processes. Additionally, use of the most conservative values can result in overly stringent local limits that place a significant burden on industrial users. Three CWS facilities rely on biological nitrification to meet ammonia effluent limits. Preliminary analysis suggested that local limits for Cu and Zn would likely be driven by the nitrification inhibition threshold. Given the wide range of inhibition levels in the EPA Guidance (0.05 to 0.48 mg/L for Cu and 0.08 to 0.50 mg/L for Zn) and the fact that CWS WRRFs have experienced influent levels above the lower end of the defined ranges with no discernible impact to the biological processes, CWS decided to conduct testing to establish site-specific nitrification inhibition levels for Cu and Zn for use in local limits analysis. Methods Testing used a modified version of ISO 9509:2006, which assesses the short-term inhibitory effect of substances on nitrifying bacteria in activated sludge over the course of several hours. The test substance is added to return activated sludge (RAS), which is spiked with a buffered ammonia substrate and aerated at constant temperature and pH while nitrate is measured to determine the rate of nitrification. Six reactors were operated concurrently, with varying levels of Zn or Cu dosed into five reactors. Each test included one control against which the nitrification rates of the dosed samples were compared (Figure 1). RAS from each of the three nitrifying facilities was tested. Nitrate was graphed vs. time (Figure 2) and nitrification rates were derived from the slopes, normalized to 20 degrees C using a temperature correction factor, and compared to the nitrification rate of the DI control. Most testing focused on levels below 5 mg/L, though several tests used doses as high as 55 mg/L. Samples were taken from several reactors at the end of each test and analyzed via ICP-MS to determine the total concentration of metals in each reactor, including the dose and background metals present in the RAS. Concentrations of metals in short-term batch tests do not directly translate to WRRF influent concentrations. Influent and RAS metals data, along with data on average primary and secondary removal efficiencies and typical summer SRTs and HRTs, were used to compute an average RAS-to-influent concentration factor for each metal at each WRRF. This factor was correlated with inhibition test results to calculate raw influent concentrations that, if sustained over time, would result in the test concentrations. Results were then fitted to a logistic sigmoidal equation to define a threshold for a response. Results Nitrification rates were normalized against controls and plotted against the concentration of Zn or Cu in each reactor (Figure 3, Figure 4). Durham and Forest Grove WRRF tests showed generally stable nitrifying activity at lower metal concentrations, with a downward trend starting around 2 mg/L for both metals. Rock Creek WRRF results did not demonstrate clear inhibition in this range, but the dataset for this facility was less extensive and included only three tests with metals concentrations above 2 mg/L. An example of the calculated raw influent response threshold curve is shown in Figure 5. Significance Published inhibition guidance may not be informative for POTWs wishing to protect biological treatment processes when establishing local limits for industrial users. Site-specific testing can be used to provide greater confidence in the local limits that are established and in their ability to protect biological processes at WRRFs.

A twin outfall relief sewer system for a major municipality is comprised of twin box structures approximately 11 LF in height and 10-12 LF in width, with average flows of 200-700 MGD. This sewer system is located below a military facility, making all inspections and repairs demand additional security considerations. During recent inspections of the twin outfall relief sewer system, CCTV footage showed areas of the sewer structure with extensive corrosion damage from microbial hydrogen sulfide (H2S). The damage caused by the H2S was so severe that the center wall between the twin box structures was missing for approximately 75 LF and much of the inner layer of reinforcement was also missing. The Owner's engineer performed structural analysis and determined the degraded portion of this structure was near collapse. Based on the as-found conditions and analysis performed, emergency remediation of approximately 910 LF of rectangular box structure was deemed necessary. The next step to minimize risk of collapse involved removal of the soil overburden in the region where the sewer system showed severe distress. The project team worked to develop a bypass system to reroute flows so permanent repairs could take place. Given the live flows within the structure, rehabilitation options needed to be selected prior to the bypass system being in place and the structure dewatered. This uncertainty regarding the condition of the structure required the repair system selected to be flexible to accommodate varying degrees of degradation. An innovative sewer rehabilitation technology was selected which involves installation of custom fabricated steel rings, HDPE interior protective layer, and a flowable grout to fill the space between the HDPE and the host structure. The design of the rehabilitation system can be adjusted based on as-found conditions, giving the project team the flexibility needed to move forward with repair design in parallel to installing the bypass and performing a more thorough condition assessment of the structure. This technology has a history of over 20 years of successful implementation in Japan with over 250,000 LF of successful pipeline repairs. This extended history along with extensive technical vetting allowed the project team to feel confident moving forward with a first-of-a-kind application in the United States. This paper will highlight the investigation, analysis, design, and emergent repair of this critical structure. Perspectives from the Owner, Engineer, and Contractor will be provided, along with insight on the options analysis process, and lessons learned throughout.

Over the past five years, the demand for engineers has surged across public and private sectors. Yet, recent graduates and early-career engineers often favor private roles, overlooking the contributions of public sector engineering. In response, the South Platte Renew (SPR) Engineering Division initiated an intern program to bridge this gap and highlight the rewards of public sector work. The SPR Engineering Intern Program aims to broaden budding engineers' horizons, providing hands-on experience in real-world problems within the public sector. The program emphasizes the Owner's viewpoint, addressing fiscal responsibility, direct impacts on waterways, political drivers, and purpose-driven leadership. Crafted over three to four months, the internship allows students to explore operations, facility maintenance, construction inspection, project management, and the multifaceted nature of engineering roles. The methodology involves insights from former interns, workshops aligning needs, and strategic scheduling connected to SPR's Vision, Mission, and Values. The internship includes technical projects, communication-focused activities, and emphasizes professionalism. Feedback sessions and dialogues with recent graduates contribute to continuous improvement, ensuring the program meets interns' expectations. To boost interns' profiles, the program includes resume-building opportunities. This not only enhances immediate job prospects but empowers interns to navigate future careers successfully. Training sessions cover treatment, communications, safety, and construction practices, aligning with SPR's specific needs. The program's success is evident in tangible job placements within the water renewal sector, addressing the need for new talent as professionals retire. The growth in interns and partnerships with universities signify the program's positive reputation. The internship's strategic alignment with SPR's mission ensures lasting contributions. Interns engage in tasks beyond the internship, such as asset management data analysis, construction inspection, and sustainability analyses, aligning with SPR's long-term goals. In the broader context, the SPR Engineering Division's internship program serves as a model for integrating academia and industry, addressing the growing demand for engineering talent in the public sector. The program's evolution reflects adaptability, ensuring continuous improvement in shaping the next generation of engineers. Looking ahead, the SPR team aims to refine and expand the internship program. By fostering partnerships, enhancing the curriculum, and incorporating feedback, SPR aims to sustain the positive impact of its internship initiative. The program not only contributes to individual engineers' growth but plays a pivotal role in advancing SPR's mission and vision. The SPR Engineering Intern Program serves as a beacon for integrating academia and industry, a catalyst for developing future engineers, and a testament to the enduring value of public sector contributions in engineering.

Many jurisdictions across the US incentivize or require private developments to implement green infrastructure (GI) as part of their stormwater management. More recently, municipalities themselves are beginning to explore how GI can be integrated into public stormwater systems, and are seeking to understand the implications and benefits of GI in the context of their distributed, predominantly 'gray' subsurface stormwater assets. In communities where the 'low-hanging fruit' opportunities (such as integrating GI into public parks and other discrete open spaces) have been largely seized, the value of GI integration into the broader public streetscape is being recognized as a potentially significant source of further benefits. Advantages of utilizing GI include enhanced pollutant removal, reduction of stormwater runoff, climate resiliency, recreational and health benefits, and the provision of ecosystem services. The implementation of GI to achieve these outcomes for discrete project sites, be they public or private, is commonplace in many urban centers. However, there exist challenges to the effective implementation of GI practices more broadly throughout the network of stormwater collection and conveyance infrastructure that cities rely on to keep their streets functioning during significant rainfall events. These include concerns about space constraints, provision of appropriate pre-treatment, maintenance requirements, jurisdictional issues between municipal departments, treatment capacity and performance during large storms. The objective of this presentation is to provide the audience with a real-world example of a practical approach to fully integrating GI components within an urban stormwater system that addresses many of the challenges noted above. The case study at the center of this presentation is part of a roadway utility and stormwater system design (see Figure 1) that WSP developed and is overseeing the construction of in Boston MA. Construction of the design is partially complete, with the urban redevelopment project currently securing final permit approvals for the remaining phases of construction. Like many urban redevelopment sites, the case study project involved overcoming some site-specific challenges, such as a relatively high groundwater table (which can make infiltration challenging), and the desire to minimize excavation given the need to treat all in-situ material as potentially contaminated. Along with these considerations, the development of the GI-integrated stormwater design to service the proposed roadways focused on three principles: 1.Treat inflows early and don't rely on the subsurface infiltration capacity of the underlying soils; 2.Provide high-flow treatment and bypass capacity in a small footprint; and 3.Make maintenance simple! A key feature of the proposed design is that catch basins are eliminated from the new streets in favor of high-flow biofiltration cells (BFCs) which are supported by pretreatment inlets that screen out trash, debris and other coarse sediments and floatables. The BFCs were intentionally utilized as inlets so as to remove upwards of 90% of the sediment from runoff before it reaches the proposed subsurface infiltration trenches, enhancing and prolonging their functionality, and thereby minimizing maintenance and the potential need for future renewal. The treatment train proposed for the roadways achieves 98% total suspended solids (TSS) removal and 95% total phosphorous (TP) removal for a 1.25-inch 'first flush' rainfall event. This is a significant runoff water quality improvement compared to the 25% TSS and 0% TP removal typically credited to standard deep sump catch basins which are commonly the only form of treatment present in municipal stormwater systems (see schematic comparison in Figure 2). Utilizing the project case study, this presentation will provide a GI implementation template and lessons learned for integrating GI components into typical urban streetscapes with approaches that maximize benefits and minimize long-term maintenance costs.

The Washington County Commissioners are expanding the sewer system in a well-established neighborhood outside of Marietta Ohio to comply with the Ohio Environmental Protection Agency's (OEPA) Findings and Orders. Devola, a Census-Designated Place has 2,639 residents per the 2020 census and is on the east side of the Muskingum River, north of the City of Marietta in southeast Ohio. Approximately half of Devola is served by a centralized sewer system also known as Phase I, while the other half consists of private septic systems, including leech fields, aerators, and holding tanks. In 2012, the centralized system's treatment facility was retired, and a new lift station and force main was built to convey sewage to nearby Marietta for treatment. One year prior, in 2011, the OEPA completed an investigation into the causes of high nitrate levels found in the Muskingum River near Devola. The investigation concluded that failing septic systems in Devola significantly contribute to the nitrate contamination in the groundwater, which is above the drinking water standard level of 10 parts per million. The OEPA also determined that the aging private septic systems in Devola are not suited for new or upgraded individual sewage disposal systems, due to small sized lots and porous soil conditions. In 2012 the OEPA sent the County the Director's Final Findings and Orders which stated that no discharge to surface waters would be allowed. A new central sanitary sewer improvement project would be designed and constructed to serve as Phase II within Devola. This new sewer system will consist of approximately 50,000 feet of sewer main network installed by open-cut trenching, boring or directional drilling; and connections to approximately 553 properties. The proposed project would also include any necessary improvements to the Phase I system, specifically enhancements to the downstream pump station due to the increased sanitary flow. At this point, the Washington County Commissioners opted to table the project as they did not have any funding to move forward with a then estimated $6M (sewer main only) project. Eventually the OEPA took the matter to court, and the County was then ordered by a judge in November 2018 to comply with the Findings and Orders. The Commissioners were now required by the OEPA and a court order to solve a very complex problem in a small community that was not only unsupportive of the project but had no means of funding such a significantly sized venture. WSP USA, Inc., a globally recognized professional services firm contracted with the County to provide planning and public outreach, engineering design, bidding and construction phase services and help with identifying funding sources to finance the project. The final design included improvements to the existing system, new sewer mains and laterals totaling over 87,000 feet (about 26.5 km) with multiple creek crossings, operational controls, new Septic Tanks with Effluent Pumps (STEP) for 560 parcels, electrical connections for the pumps, abandonment of the existing septic tanks, and site restoration. The design firm assessed various collection systems as part of the preliminary design and determined that use of a pressurized system with STEPs at each residence would ultimately save the client upwards of $5.8M in construction costs. This is due to the depth and subsequent restoration a gravity sewer system would require. The new system will use horizontal directionally drilled mains, ranging in size from 2 to 6 inches, for timely and minimally evasive conveyance to Phase I. The pressurized system has many advantages over traditional gravity, and in the future more communities may opt for this type of system. By using horizontal directional drilling, installation costs will be kept to a minimum, often lower than conventional gravity systems. Other advantages include no inflow and infiltration into the system, as well as replacement of manholes with low-cost valves and clean-outs which are spaced further apart. These cost savings are significant and ultimately led to successful implementation of the pressurized sewer plan in Washington County. To assist the County connect with the affected residents and businesses, the design firm developed a website to reach them more effectively. The status of planning, public comments, past meeting content, and future meeting dates could be quickly disseminated to the residents. Assistance was also provided to the County in identifying potential grants and loans through such organizations as the Ohio Public Works Commission, Water Pollution Control Loan Fund, the U.S. Department of Agriculture's Water and Waste Disposal Loan & Grant Program, the State of Ohio, and the US Army Corps of Engineers. In total nearly 75% of the construction cost was secured through grants and funding assistance, while the remainder of the funding was reached through a low-interest OEPA loan. The project was bid in April 2022 and awarded to RDR Utility Services Group of Clarksburg West Virginia for a sum of $14.5M. Construction commenced in the summer of 2022 and is currently about 65% complete. Final completion is expected in the winter of 2024.