Overcoming Operations and Maintenance Challenges in Siphons

Some of the more complex pipes that reside within the wastewater collections system are known as siphons/depressed sewers and are often referred to in the field as 'bellies' or 'sags.' Such systems typically navigate wastewater flow in pipelines that are near bodies of water, subways, tunnels, and other fixed utilities. These lines are constructed when traditional gravity design is not permissible, and a continuous grade cannot be maintained. Flow navigates the siphon pipe until it reaches pressurized flow and often creates foul odors which can be minimized by air lines. Siphon design allows for single barrel, double barrel or multi barrel and the number of barrels is typically related to the agency's requirements on hydraulic efficiency, maintenance, emergency events, and bypass requirements. Additionally, siphon design is critical for the future life span of the pipe due to its impact on operations. A poor design can lead to blockages, sediment build up and direct impacts on minimum velocities that are critical in siphons. For operations and maintenance this is critical because Siphon debris levels must be monitored closely to evaluate future needs for additional barrels, increased maintenance requirements and necessary repair work. In this abstract we concentrate on different operations and maintenance approaches on various siphons and the economic impact it can create for the utility owner and contractors. The first approach that will be discussed will be centered around cleaning siphons that have not been maintained and where minimal information is available. Secondly, the methodology of inspection and the various means that can be attempted dependent on the technology used. Lastly the combined approach of both inspection and cleaning will be discussed and evaluated. One of the most expensive approaches is often seen as is one in which the contractor blindly attempts to clean a sewer line (whether it be a siphon or not) without the known conditions of the pipeline. Not only is this a high-risk module but it is one where variables such as the structural integrity of the pipe, sediment levels, unknown debris types, and so much more are put into question. This approach will discuss a few siphons in San Bernardino that where maintained under a clean first approach. An inspect first approach can often be the least economically bearing approach because it is one that assumes it has minimal information from the start. This is because this method creates the information the owner can utilize to provide details about the siphon. Sonar and CCTV will be discussed and how the different technologies provide for varying deliverables and the limitations of each. Finally, one of the most comprehensive approaches is one in which the siphon is inspected, and the asset is assessed providing tangible details so that the line may be properly cleaned at a price that is well evaluated. This method will discuss the success of an inspect/clean siphon project in San Diego. This presentation will provide much needed information for a topic that has very limited information. This is because nationwide siphons are sometimes not maintained due to costs and or limited staff already strained by the primary collections system. The specialized work is one that is becoming more necessary and vital due to the aging assets and the imperative need to avoid emergencies on them.