Advanced Analysis Guides CSO Work along the Connecticut River

Advanced Analysis Guides CSO Work along the Connecticut RiverAbstractThe City of Holyoke, Massachusetts sits on the western bank of the Connecticut River, just north of Springfield. Incorporated as a city in 1873, Holyoke was once the world's leading writing paper production center, relying on the abundance of water and hydroelectric power provided by the Connecticut River. As is common in historically industrial New England cities, Holyoke relies on a patchwork system of infrastructure spanning many eras to provide wastewater collection and drainage. Currently, approximately 70% of their collection system remains combined. Under regulatory pressure from the United States Environmental Protection Agency (USEPA), Holyoke is working on implementing a Long Term Control Plan (LTCP) to address combined sewer overflows (CSOs), and next on the list is separation of the 150-acre River Terrace Drainage Area, which stretches from the bank of the Connecticut River on the east to the I-91 Corridor to the west; and from Riverview Terrace at the north end to Hillview Road to the south. Having drafted an LTCP in 2000, Holyoke has made some progress on CSO abatement goals over the past 20 years. However, significant challenges persisted, and the USEPA issued a partial consent decree in 2019, prompting the first update to the LTCP since 2000. In the 2019 update of the LCTP, a sewer separation project was recommended in the River Terrace neighborhood of the City. This recommended project was estimated to reduce annual CSO volume by 58 MG, roughly 35% of Holyoke's average annual discharge volume (2011-2018). Separation of the River Terrace neighborhood was not a new idea — it had been identified in the 1988 Lower Connecticut River Phase II Combined Sewer Overflow Study as an integral part of Holyoke reaching 90% CSO volume abatement. The project had slipped in priority in the intervening years, falling to the late 2030s in the 2019 LTCP Implementation Schedule. A new Consent Decree issued in the Spring of 2023 has caused the River Terrace Separation Project to jump the line, requiring project completion by 2027. Design had begun in 2021 but faltered. The City decided to change consultants during design, hiring Woodard & Curran to reevaluate the project approach and design. The project area is residential, developed in the late 1800's, and consists of tightly nestled residences on narrow, curving streets. Due to uncertainties around the capacity, location, and condition of the existing combined sewers, as well as a spiderweb of existing utilities, the team determined that the problem demanded a more thorough investigation and analysis. Differences between the documentation obtained by W&C as well as observed conditions, and in some cases the lack of documentation led the design team to conduct extensive field investigations, consisting of multiple rounds of field survey, CCTV investigations, flow metering, and field investigation by design engineers. The information collected was then used to develop a coupled 1D/2D combined sewer model on the InfoWorks ICM platform. Surveyed topography and publicly available land use and soils data were used to assemble the 2D domain, while existing and proposed pipe networks, including inlet locations, were used to assemble the 1D domains for existing and proposed conditions. This model provides a more sophisticated and robust tool for analysis of the hydraulic capacity of the combined sewers and therefore a more complete understanding of what is required to maintain or improve the level of service. Using the model, the design team was able to clearly identify the required capacity of the separated system and account for differences between documented and field-validated conditions. In conjunction with the investigation data, the model was also used to identify how much of the existing infrastructure could be kept intact to reduce project costs. In 2019, when the project was identified, the total cost was estimated at 16 million. With the first phase, constituting about half of the total separation, currently estimated at 12 million, any opportunities for savings must be explored. In one location, results of detailed analysis obviated the need to replace 1, 200 feet of 30-inch pipe, saving over a million dollars. As a community looking at significant wastewater infrastructure investments in the coming years and a projected high burden on ratepayers, it is crucial to leverage attention to detail with the right analysis tools. This project is an example of the challenges that arise throughout a combined sewer separation project, beginning with planning and continuing through final design. The presentation will discuss specific design issues encountered throughout the project and how they were addressed. In particular, it is important to not underestimate sewer separation costs by assuming more infrastructure can be reused than can in reality. Attendees will see a pattern that helps anticipate the challenges and the tools that can be applied to navigate them, and they will take away the importance of using the right assessment tools for making decisions about significant investments. This paper was presented at the WEF Collection Systems and Stormwater Conference, April 9-12, 2024. SpeakerTrainor, KevinPresentation time16: 15: 0016: 45: 00Session time13: 30: 0016: 45: 00SessionLocal Case StudiesSession number23Session locationConnecticut Convention Center, Hartford, ConnecticutTopicClimate Change Adaptation, Collection Systems, Combined Sewer Overflow, Combined Sewer System, Construction, Deep Sewer Tunnel, Design Storm, Infiltration/Inflow, Precipitation Frequency, Sewer Separation, SSO Reduction, Stormwater Case Study/Application, Surface Water, Utility Management, Water QualityTopicClimate Change Adaptation, Collection Systems, Combined Sewer Overflow, Combined Sewer System, Construction, Deep Sewer Tunnel, Design Storm, Infiltration/Inflow, Precipitation Frequency, Sewer Separation, SSO Reduction, Stormwater Case Study/Application, Surface Water, Utility Management, Water QualityAuthor (s) Trainor, KevinAuthor (s) K. Trainor1Author affiliation (s) Woodard & Curran, Inc. 1SourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Apr 2024DOI10. 2175/193864718825159340Volume / Issue Content sourceCollection Systems and Stormwater ConferenceCopyright2024Word count10