As one can easily see, manhole rehabilitation offers the most cost effective means of eliminating upwards of 30% of the total quantifiable I/I.
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.
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.