Sewer Siphon Assessment and Air Jumper Design

In response to customer complaints about sewer odor, Orange County Sanitation District (OCSD), California launched a project to investigate the ventilation requirements of existing sewer siphons, to verify adequacy of existing air jumper operation, and determine the need for new air jumpers or additional air jumper capacity. The challenge was assessing sewer siphon air jumper adequacy without clear industry standards or guidance for comparison and to then develop air jumper sizing guidelines and recommendations for retrofit replacement or addition of air jumpers at 17 of the existing 87 OCSD sewer siphon locations.A literature search for sewer siphon air jumper sizing guidance was conducted. For each of the 17 sewer siphons studied: siphon inlet and outlet structures were inspected; sewer flow was measured; headspace air pressure or vacuum was measured; air flow into or out of the upstream and downstream siphon structures was measured; and dissolved and headspace hydrogen sulfide levels were measured. Relationships were theorized and developed between: depth of wastewater flow in the sewers; velocity of wastewater flow; sewer headspace airflow rates; and sewer headspace pressure or vacuum with manhole covers in place. General design guidelines for sewer siphon air jumpers were developed and recommended and these guidelines were applied to the field data for each of the studied 17 siphons. Sewer siphon air jumper retrofit replacement or additions are currently in the final design phase with construction scheduled to start in February 2007.