Lateral Rehabilitation - Start to Finish

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Abstract:

Infiltration and Inflow (I/I) is a major contributor to sanitary sewer overflows (SSOs) occurring in collections systems throughout the country. To reduce the frequency and severity of SSOs, many utility owners are embarking on sewer system rehabilitation programs. These rehabilitation programs often focus on mainline sewers and manholes, while ignoring laterals due to their limited accessibility and private ownership. Various publications indicate that sanitary sewer laterals account for up to 50% or more of the total I/I in a collection system. Television observation following mainline rehabilitation has shown significant flows can enter the sewer via unrehabilitated lateral connections. Lateral inspections have also shown cracks, roots and other defects that contribute to I/I of similar frequency as observed in mainline sewers. Furthermore, as a result of mainline sewer and manhole rehabilitation, the groundwater table may rise and generate infiltration through laterals that previously generated minimal leakage. Therefore, to achieve the most significant reductions in I/I in a catchment area, lateral rehabilitation must be included as part of the sewer rehabilitation program. This poster discusses the essential components of a successful lateral rehabilitation program with the primary goal of significantly reducing I/I.

In a wholistic sewer system rehabilitation approach, catchment areas are typically prioritized by areas with the most leakage as determined by one or more of the following techniques: nighttime flow weiring, flow metering or smoke-test observations. Once a catchment is selected for wholisitic rehabilitation, the type of rehabilitation of the mains and laterals is determined based on structural condition (observed through television inspection), life-cycle cost analyses, design life objectives, anticipated effectiveness of the rehabiliation method, and constructability and social impact concerns. Various methods and technologies are considered for lateral rehabilitation, including pressure testing and packer injection of tap connections (grouting), “Top Hat” or saddle liners, T‐LinerĀ® Shorty liners, full cured-in-place lateral lining (CIPLL) and complete lateral replacement by open-cut or pipebursting. Where maximum I/I removal is desired while minimizing social disturbance, CIPLL is often selected as the primary method for lateral rehabilitation.

Many CIPLL technologies require external access points, typically a external cleanout, to install the liner. In older developments, where a majority of rehabilition occurs, cleanouts either were not installed during original construction or mature landscaping makes their location difficult to acertain during site visits. To locate existing cleanouts or to site locations for new cleanouts, sonding with a side-launch CCTV camera is used to mark out the path of the lateral on the ground surface and document defects that may prevent successful installation of the CIPLL. Prior to initiating sonding field work, research is performed to determine widths of existing right-of-ways and easements, as well locations of other buried utilities in the right-of-way. If an existing cleanout is not located during sonding fieldwork, two cleanout locations are sited for each property. The first location is in the right-of-way or easement, which is the default location, and the second location is sited on private property. After sonding is complete, Lateral Rehabilitation Agreements (LRAs), which include a figure depicting the proposed new cleanout location on private property or documentation of existing cleanout located on private property, are prepared for each property. If accepted and executed by the property owner, the LRA provides the legal right for the utility to access the private property to install the cleanout and CIPLL. With the mailing of LRAs to property owners for their review and execution, a public meeting is announced to respond to questions from the public. Topics of discussion at the public meeting include review of proposed work, notification, construction and restoration procedures, benefits of allowing the utility to enter private property to perform the work, potential impacts of the work, explanation of the work that will be conducted if the LRA is not returned and a tentative construction schedule. If LRAs are not received from property owners by a specified date, the cleanout is installed in the default location and the lateral is lined to this cleanout.

In one project area, preliminary rehabilitation effectivenss results of both mainline and lateral rehabiliation show a I/I peak flow rate reduction of 67% and I/I total volume reduction of 61%. Ongoing flow monitoring activities are expected to illustrate realtive I/I reductions achieved from staged implementation of mainline, lateral and manhole rehabilitation within selected target catchment areas.
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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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