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State of Technology for Rehabilitation of Wastewater Collection Systems

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State of Technology for Rehabilitation of Wastewater Collection Systems EPA/600/R-10/078 | July 2010 | www.epa.gov /nrmrl State of Technology for Rehabilitation of Wastewater Collection Systems Office of Research and Development National Risk Management Research Laboratory - Water Supply and Water Resources Division United States Office of Research EPA/600/R-10/078 Environmental Protection and Development July 2010 Agency Washington, DC 20460 State of Technology for Rehabilitation of Wastewater Collection Systems State of Technology for Rehabilitation of Wastewater Collection Systems by Dr. Ray Sterling, P.E., Jadranka Simicevic, Dr. Erez Allouche, P.E. Trenchless Technology Center at Louisiana Tech University Wendy Condit, P.E. Battelle Memorial Institute Lili Wang, P.E. ALSA Tech, LLC Contract No. EP-C-05-057 Task Order No. 58 Ariamalar Selvakumar, Ph.D., P.E. Task Order Manager U.S. Environmental Protection Agency Urban Watershed Branch National Risk Management Research Laboratory Water Supply and Water Resources Division 2890 Woodbridge Avenue (MS-104) Edison, NJ 08837 National Risk Management Research Laboratory Office of Research and Development U.S. Environmental Protection Agency Cincinnati, Ohio 45268 July 2010 DISCLAIMER The work reported in this document was funded by the U.S. Environmental Protection Agency (EPA) under Task Order (TO) 58 of Contract No. EP-C-05-057 to Battelle. Through its Office of Research and Development, EPA funded and managed, or partially funded and collaborated in, the research described herein. This document has been subjected to the Agency’s peer and administrative reviews and has been approved for publication. Any opinions expressed in this report are those of the authors and do not necessarily reflect the views of the Agency; therefore, no official endorsement should be inferred. Any mention of trade names or commercial products does not constitute endorsement or recommendation for use. ii EXECUTIVE SUMMARY Introduction The variety of tools available to the sewer utility engineer today is remarkably different than it was during the 1960s. However, the average rate of system rehabilitation and upgrading within the U.S. is still not adequate to keep pace with increasing needs, quality demands, and continually deteriorating systems. The objective of this report is to summarize the current status of the development and application of repair, rehabilitation, and replacement technologies for wastewater collection systems. This report covers technologies applicable to sewer mainlines, laterals, manholes, and other appurtenances such as lift stations. The emphasis of the report is on trenchless technologies, which do not require full excavation of the buried asset in order to carry out the work. These technologies have made a significant penetration into the U.S. market with estimates of the proportion of rehabilitation work carried out using trenchless techniques ranging up to 70% in the sewer sector (Carpenter, 2009). There is still considerable room for improvement in existing trenchless technologies and/or in the development of new trenchless technologies. Such improvements or new technologies offer the chance to make the investments in rehabilitation more effective and to extend the ability of utilities and local governments to fix larger portions of their systems with current funding levels. A secondary benefit is to increase the political and public will to spend additional money on fixing this problem. Characteristics of Gravity Sewer Systems In the U.S., there are approximately 16,000 sewer systems serving 190 million people and incorporating approximately 740,000 miles (1,190,660 km) of public sewers, plus 500,000 miles (804,500 km) of private lateral sewers. The term “sewer main” typically refers to the publicly owned collection lines that collect the sanitary sewage from individual properties, convey it to a treatment plant, and release it into a receiving body of water. Most sewer systems are laid out as gravity sewers, which transfer their flow under gravity in sloped sewers that are only partially filled under normal operating conditions. Historically, many sewer systems were designed as “combined” systems that handled both sanitary sewage flow and stormwater drainage flows. The advantages were that storm flows would help to flush the system clean. The disadvantages were that during periods of high rainfall, it was necessary to allow excess flows to discharge into waterways through overflow structures. These overflows, known as combined sewer overflows (CSOs), were untreated, but diluted sewage. Over time, it became an unacceptable pollutant to the receiving waters. Such overflows are no longer permitted as a normal operating practice and many newer systems have been designed as “separated” systems with separate pipe networks for sanitary and stormwater flows. In cases where a combined system existed, new “interceptor” sewers have been designed to capture the overflows from combined systems and convey, store, and treat these flows, as appropriate, in the particular sewerage system. The historical layout of gravity sewer mains has been strongly tied to topography, with sewers starting at the high points of a catchment area and following the natural drainage paths to a larger body of water where the sewage treatment plant was placed. In cities with a flat topography, a gravity sewer system has typically been designed with pipe sections installed to gradient via open-cut construction until the depths of excavation became uneconomical. At this point, a pump or lift station is installed to lift the sewage into a new pipe section, starting at the minimum depth of burial and flowing again via gravity either to the treatment plant or to another lift station. iii Sewer laterals are the portion of the sewer network connecting individual properties to the public sewer network, but with some features (e.g., size of pipes, materials used, construction practices, and particularly ownership responsibility) that are different from the rest of the sewer collection system. Manholes are provided in sewer systems to help maintain and clean sewer pipes. Typically, they are provided at intersections of two or more mainline sewers, at changes in direction of sewer lines, and at regular intervals along a mainline. Manholes are typically spaced approximately 300 feet (91 meter) apart, but can be less than 100 feet (30.5 meter) or as far as 500 feet (152.4 meter) apart. Using these values, the number of manhole structures in the U.S. can be roughly estimated at over 12 million. Other structures that are part of a sewer collection system include pump/lift stations, valve or diversion structures, overflow structures, and drop shafts. There are also mechanical and sensor components, such as pump units, pump control systems, and flow monitoring stations, but these latter mechanical systems are not addressed in this report. Renewal Technologies for Sewer Mainlines In this report, the term “renewal” of a system is treated as the goal, while repair, rehabilitation, and replacement are methods to maintain performance and extend life to keep the system functioning at an acceptable level and at a minimum life-cycle cost for the foreseeable future. Repair actions are used either to restore the sewer to an operating condition or to deal with localized deterioration. Rehabilitation may include internal coatings, sealants, and linings used to extend operational life and restore much or all of the pipe’s hydraulic and/or structural functionality. The focus of this report is on techniques used without an open-cut excavation to fully expose the sewer line. Replacement technologies essentially replace the existing pipe with a brand new pipe that provides a new conduit, but is not dependent on the existing host pipe for its structural performance. Repair techniques include internal and external repair sleeves, short sections of cured-in-place liners and robotic repairs using in-pipe robots. Rehabilitation techniques include lining using sliplining, a variety of cured-in-place liner approaches and close-fit lining technologies, plus grouting approaches to seal leaky pipes that are otherwise structurally sound. Replacement techniques include pipe bursting and related techniques that will install a new pipe on the same alignment as the existing pipe, as well as conventional and trenchless methods to replace existing pipe on a new alignment. The characteristics of renewal technologies for sewer mainlines, with emphasis on trenchless methods of rehabilitation, are described in this report. Appendix A provides general descriptions of each method, with detailed datasheets for representative technologies. The most commonly used technique for rehabilitation is cured-in-place lining, but several other technologies are available in order to provide solutions to a wide range of site constraints in the existing sewer system. Renewal Technologies for Laterals, Manholes, and Appurtenances Sewer laterals can be considered as merely additional pipe segments connecting building properties to the mainline sewers; however, laterals have a number of physical and administrative conditions that make both assessment and renewal programs more problematic than for the mainline sewers. The physical conditions include small diameters, frequent diameter changes, multiple bends, poor installation quality (especially at the junction with the mainline sewer), and blockage/damage caused by tree roots. Legal and administrative difficulties with the renewal of sewer laterals include the interaction between public funding
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