State of Technology Report for Force Main Rehabilitation, Final Report (EPA/600/R-10/044) March 2010
Force mains that carry sewage flows under pressure represent a special set of challenges for sewer rehabilitation. Force mains represent about 7.5% of the wastewater system and they typically use materials that are not commonly used in gravity sewer systems. Ductile iron (DI), cast iron (CI), steel, and concrete pressure pipe are all material types that are frequently used for sewer force mains, especially in larger diameters. All of these materials are susceptible to both internal corrosion from the sewage flow (liquid and gaseous states), as well as external corrosion due to the environment in which the pipe is buried. Historically, the most common renewal technology employed has been to replace the main using open cut construction. Part of the reason for that choice has been a lack of rehabilitation technologies appropriate for sewer force mains. There is a wealth of technologies available for gravity sewers, but the field has been limited for pressurized systems. Fortunately, that situation is changing as more vendors recognize the growing opportunity in sewer force main rehabilitation. The other reason for replacement is that sewer force mains tend to have a fairly high consequence of failure. A rupture of a sewer force main could release millions of gallons of raw sewage into the environment posing significant health risks to the general public. Cleanup costs can be staggering. As some of the newer rehabilitation technologies develop a positive track record of use in sewer force mains and confidence in their design approach and installation process strengthens, more utilities will be willing to consider these trenchless technologies as potential renewal solutions. Trenchless methods have proven themselves to be cost-effective for gravity sewer mains, especially when both direct and indirect costs associated with a replacement program are considered. A similar outcome is expected for sewer force mains once data on the effectiveness and longevity of these technologies and materials and life-cycle costs become more readily available. Recognizing that there would be some cross-over amongst the various rehabilitation technologies common to water mains and gravity sewers, a series of technology-specific datasheets were created for each identified rehabilitation technology deemed relevant to sewer force mains and are included as Appendix A of this report. An effort was made to collect representative cost information, but often only limited cost data were available.
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