Plan the Work, Work the Plan: Long-term I/I Mitigation in Practice

Plan the Work, Work the Plan: Long-term I/I Mitigation in PracticeAbstractThe City of Beverly, Massachusetts is committed to providing exceptional sewer service to its residents while also reducing inflow and infiltration (I/I) to meet DEP I/I guidelines, lower sewage treatment costs, and minimize the risk of sanitary sewage overflows. The City has strategized with Dewberry Engineers Inc. to achieve these goals through the development and implementation of a holistic I/I capital improvements program (CIP). This program is built on informed decision-making, leveraging field collected data to pinpoint and address the City's most critical sewer infrastructure needs. As a background, the City of Beverly (the City) is a coastal New England community, located about 45 minutes north of Boston. Formally incorporated in 1668, it is one of the oldest communities in America. Rich in history and culture, the City is recognized as the launching point for the U.S. Navy's first armed schooner, the U.S.S. Hannah in 1775. Today, the City has a thriving population of 42,500 people and boasts a couple of notable colleges (Endicott College and North Shore Community College) and a regionally recognized business center (Cummings Center). The City is also a haven for those trying to escape the hustle and bustle of Boston during summer months. About 120 years ago, the City began construction of its citywide sewer system using primarily vitrified clay pipe, the choice material of the time. Most of this pipe is still in the ground today, despite having far exceeded its useful life (50-60 years). Cracked pipe, make-shift lateral connections, and joint offsets due to decades of soil settling have created major infiltration issues in the system, especially after wet weather events. The City's sewer manholes are equally as old and are constructed primarily with brick and concrete mortar material. Over time, sewer gases have eaten away at much of this concrete mortar, creating additional groundwater entry points and compounding the issue of infiltration. The City also faces chronic inflow problems, in large part due to illicit sump pump connections. Most houses in the City have underground basements, some of which are equipped with sump pumps connected directly to the City's sanitary sewer system. When groundwater rises due to continuous wet weather events, typically in the spring season, these sump pumps activate to keep people's basements from flooding. This influx of clean groundwater to the City's sewer system skyrockets the wastewater volume being sent to the regional treatment facility. Figure 1 shows the effect of a heavy rainstorm on sewer flows for a particular sewer subsystem, prior to any rehab or repair improvements. This figure captures the magnitude of the I/I issue that the City faces. For this particular storm, sewer flows more than triple in volume. Also, note the time it takes post-storm for sewer flows to return to normal, 4+ days. In 2017, the City orchestrated a city-wide sewer flow metering effort to quantify and assess I/I volumes generated in each of its 27 sewer subsystems. With this information, the City ranked its subsystems relative to one another based on each subsystem's I/I contribution. Since then, the City has been systematically working its way down the ranked list of subsystems, investigating and addressing I/I and other sewer deficiencies in its 'worst' subsystems first. This presentation will explain the tried and true methodology that the City uses to identify and tackle necessary sewer improvements and reduce I/I from wet weather events. The City's approach starts with targeted field investigations including flow metering, flow isolation, smoke testing, closed-circuit television (CCTV) inspection, manhole inspection, and property surveys. As data is collected, it undergoes detailed engineering review and assessment, which informs the design of sewer rehabilitation or open-cut repair projects. Once a project is designed, it is publicly bid and constructed with an appropriate level of engineering oversight to ensure quality construction and community satisfaction. The process does not stop there, though. As construction projects are completed, additional post-construction inspections are performed to verify the desired outcome has been achieved. Findings from these post-construction inspections may reveal additional work is needed. This additional work is then tacked onto future construction projects. The City's approach is cyclical in this way: field investigations inform project designs, which lead to construction projects. The success of a given project is then verified by follow-up field investigations that may or may not dictate additional work requirements. Figure 2 shows a map with pre- and post-construction flow isolation values for a particular subsystem where sewer rehabilitation improvements took place. This map shows how, in most cases, flow isolation values decreased following completion of the rehabilitation project. However, there are particular pipes upstream or downstream of rehabilitated sections, that saw their flow isolation values increase. This is likely due to groundwater migration. These pipes have since been incorporated into the design of another sewer rehabilitation project. As part of this presentation, Dewberry will share a history of sewer improvements in the City and how the aforementioned strategy became the current, working standard for the City's I/I CIP. Examples from sewer subsystems in which work has recently been completed will be shared along with some of the complex challenges and unique opportunities that stemmed from implementation of the I/I CIP. The presentation will also discuss efforts that Dewberry has made to quantify I/I reduction of past completed projects, including a deep dive on a recent analysis using a sophisticated engineering software, Sliicer, developed by ADS Environmental, Inc. Lastly, Dewberry will talk about the future of the City's I/I CIP, particularly how asset management is shaping the way the City thinks about sewer data. The intent of this presentation is to provide hope and direction for communities that are unclear where their sewer program is headed and what their next steps should be. The City of Beverly, through thoughtful leadership and planning, has developed a strategy for its I/I CIP that is working to stabilize their sewer system to the impacts of wet weather events. While all of the City's sewer issues cannot be addressed today, the City has a road map, and through persistence and staying the course, it will be able to maintain its system at a high-level well into the future.This paper was presented at the WEF Collection Systems and Stormwater Conference, April 9-12, 2024.SpeakerBateman, MilesPresentation time10:15:0011:45:00Session time10:15:0011:45:00SessionInflow and InfiltrationSession number30Session locationConnecticut Convention Center, Hartford, ConnecticutTopicCIP Development, Collection Systems, Infiltration/Inflow, Manholes, Rehabilitation, SSO Reduction, Utility ManagementTopicCIP Development, Collection Systems, Infiltration/Inflow, Manholes, Rehabilitation, SSO Reduction, Utility ManagementAuthor(s)Bateman, MilesAuthor(s)M. Bateman1Author affiliation(s)Dewberry Engineers, Inc. 1SourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Apr 2024DOI10.2175/193864718825159404Volume / Issue Content sourceCollection Systems and Stormwater ConferenceCopyright2024Word count12