A primer on sanitary sewer rehabilitation: Repair and renewal can reduce extraneous flow and address structural defects

Extraneous water may enter the pipes from unintended sources, either from surface water, groundwater through defects, or direct illicit connection. These defects are pipe system deficiencies resulting from system aging, structural failure, lack of proper maintenance, and/or poor construction and design practices. They can include conditions such as broken pipe; leaking joints; manhole lids with...

State-of-the-art water sector experience indicates that before investing in sanitary sewer capacity expansions to handle excessive I/I, it is prudent to improve sewer system structural conditions to realize practical levels of I/I reduction. Only then should a utility or sewer district consider supplementing with right-sized conveyance and/or storage and downstream treatment systems. Asset...

Sewer rehabilitation can be considered both repair and renewal to reduce extraneous flow and address structural defects. Rehabilitation is different from system replacement in that repairs selectively target I/I sources and structural defects rather than complete replacement of pipes and/or manholes. Not all sewer defects cause capacity restrictions or are considered I/I sources.

With many options available to rehabilitate sewers, the conditions affecting sewers should be considered before deciding on a rehabilitation method. Factors to consider when selecting a rehabilitation method include, but are not limited to,

Sewer pipe failure most often results from lack of maintenance. Three stages of decay warrant definition and are a direct result of I/I.

Pipe linings are tight fitting and installed continuously from one access point to the next. Linings provide structural renewal of the pipe barrel, improve the performance of the existing sewer, and are appropriate for various pipe sizes and shapes.

In-situ spray or spun cast coatings or structural solutions may be used to extend the life of an existing sewer by increasing its strength or protecting the existing surface from corrosion or abrasion. Coatings also may be used to improve hydraulic performance.

It is common for multiple technologies and more than one methodology to be deployed on a mainline sewer rehabilitation project. Most lining projects require very little or no infiltration during the application as well as flow diversion and pipe cleaning. Coating projects may require flow diversion and specific surface preparation, depending on whether a bond to the host pipe or structure is...