Draft Infiltration and Inflow Report March 1998

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system which are structurally defective, and require rehabilitation. Incorporating the television tapes into a central library of system information will allow the rate of system deterioration over time to be determined. Annual televised footage will total approximately 200,000 feet, at an estimated approximate cost of $600,000. This cost is based on typical cleaning and televising costs by a contractor. c) Cleaning System-wide cleaning is recommended once every three years. This schedule does not include any emergency cleaning or blockage removal. As a part of a preventive maintenance program, scheduled cleaning of the pipelines seeks to prevent the development of blockages. Blockages may be physical or hydraulic, so named for their causes. A physical blockage is caused by a buildup of solidified grease, detergents, or any kind of solid debris from the wastewater, held in place by some physical defect--a root mass, a protruding tap, a large crack or break, settled object(s) too heavy to move with the flow, or a discontinuity because of an offset joint. Grease can also build up on the wall of the pipe by simple adhesion, completely obstructing the pipe. A hydraulic blockage results from inefficient design, where the angle of converging flows causes turbulence, allowing heavier debris to settle out of the wastewater. The cause of hydraulic blockages is less often poor original design than later extensions to accommodate additional tributary azea. In such cases, frequent scheduled cleaning tends to prevent blockages from developing. The schedule for routine pipeline cleaning depends on the grade of each line, the type of area served, and the past history of collection system performance with the latter being the most important criterion. A pipe laid at a steep grade with high velocity flow normally presents fewer problems than one on a flat grade. In residential areas the increased use of garbage ADS Environmental Services, Inc. IV-16