UCT International Conference and Exhibition Track III-A. Assessing and Understanding Sewer Pipeline Deterioration. Rod Thornhill, PE White Rock Consultants Dallas, Texas. Proactive Renovation and Replacement. The pavement
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UCT International Conference and Exhibition
Assessing and Understanding Sewer Pipeline Deterioration
Rod Thornhill, PE
White Rock Consultants
Management industry has used a history of condition assessment to justify cost-effective proactive renovation
History of Sewer Pipe Installation
Miles of Pipe
Total Approx 520,000 Miles
EPA Gap Analysis
Average Age of Sewer Pipes
Age in Years
EPA Gap Analysis
Inverted Syphon / Force Main
Under anaerobic (septic) conditions, sulfate present in the wastewater is converted to sulfides within the slime layer inside the pipe. Force mains generally flow full with little aeration therefore likely points for sulfide production. Dissolved oxygen levels must be near zero in order for sulfide production to occur.
Discharge manhole/gravity sewer
Sulfides in the wastewater are released by turbulent conditions at discharge point into the sewer atmosphere and form hydrogen sulfide gas (H2S).The H2S condenses on the pipe surfaces and is converted by bacteria into a weak sulfuric acid. The sulfuric acid attacks concrete and metal surfaces.
Under anaerobic (septic) conditions sulfate present in the wastewater is converted into sulfides within the slime layer. Sewers with laminar flow therefore little aeration are most susceptible to low dissolved oxygen levels
Turbulence releases dissolved sulfides into the sewer atmosphere in the form of hydrogen sulfide (H2S). The H2S then condenses on sewer surfaces in the form of sulfuric acid. The sulfuric acid attacks cement based materials and metals.
“American sewerage practice is noteworthy among the branches of engineering for the prepondering influence of experience rather than experiment upon the development of many of it’s features, apart from those concerned with treatment of sewerage”
“The amount of capital required to put up a small plant for making cement tile and pipe is so moderate that a large number of these little works have been built. Owing mainly to lack of skill, working capital, or both, much inferior pipe has been produced in these small plants, and this poor product has prejudiced many engineers against all cement pipe”
“Every reported case of failure in drainage which we have investigated, has resolved itself into ignorance, blundering, bad management, or bad execution” Gisborne
Definition:An approach that uses continual condition assessment, preventive maintenance, and renewal to provide an acceptable level of service for all pipelines, in perpetuity
Process of Pipeline
5-10% of System
10-15% of System
All Other Sewers
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