The Problems:
Infiltration, Fatigue and Corrosion

Infiltration
Overburdened treatment plants, increased treatment costs, surcharged lines and environmental pollution are the results of infiltration. For years, efforts to reduce or correct infiltration and its associated problems have concentrated on rehabilitating the mainlines, even though manholes and other underground structures commonly account for 30 to 50 percent of a system's infiltration  typically occuring at manhole rings, through loose mortar and precast joints and around mainline and stubout connections.

Graph 1 illustrates the average amounts of quantifiable I/I occurring in the various components of a sewer collection network, as well as the typical cost associated with rehabilitating each of these components.

As one can easily see, manhole rehabilitation offers the most cost effective means of eliminating upwards of 30% of the total quantifiable I/I.
Corrosion
Sulfide-rich effluents, a warm, humid environment and long retention times create the perfect conditions for microbiologically induced corrosion (MIC). MIC is the principal cause of corrosion in a municipal sewer system. These microorganisms metabolize elemental sulfur oxidized from H2S sewer gas and produce sulfuric acid as a waste product which then attacks the substrate. This sulfuric acid can quickly destroy ordinary concrete-based materials in a municipal sewer system.
Structural Fatigue
Subsidence from traffic loading, shifting and expanding soils, temperature variation and cyclic ground water loading seriously weaken manholes and other sewer system structures. Over time, ground water will find its way through fatigue cracks and weakened joints, leading to further deterioration of the structure. Fallen bricks and mortar can block the sewer flow, and may eventually lead to collapse, seriously endangering the surface and surrounding environment.

P.O. Box 123 Ada, MI 49301 * Phone 800.544.9053 * Fax 888.796.2653  * Email ieq@trenchless.org