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Implementing New Design Standards and Field Measurements for Air Jumper Design

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Orange County Sanitation District (OCSD) conducted field investigations due to odor complaints from the public in the vicinity of 16 sewer siphons. Based on air flow rate and pressure or vacuum measurements at those siphons, a new sewer air jumper sizing design standard was developed to transport foul headspace air from the upstream side of hydraulic blockage, caused by the inverted sewer siphons, to the downstream side. Air jumpers designed according to this standard prevent upstream headspace pressurization that would otherwise cause odorous foul air emission. This paper presents this newly developed method for air jumper design, unique design elements for this project's air jumpers, and the results of field measurements made at the newly constructed air jumpers to determine the adequacy of this new air jumper design standard.

The 16 OCSD inverted sewer siphons included in this project range in size from 15 to 60-inches in diameter. These siphons typically cross under large storm drain box culverts within heavily congested, multi-lane street intersections located in eight different cities in Orange County, California. These 16 inverted sewer siphons were found to have non-existent or inadequately sized air jumpers causing sewer headspace pressurization and odor emission.

Office research, extensive field data collection and inspection, and preparation of the Preliminary Design Report (PDR) were completed between March and October 2005. Pre-project field conditions were measured and mitigation measures for these 16 sewer siphons were developed in the preliminary design phase of work. Final design of this odor mitigation project was completed in May 2007. Construction of the new air jumpers based on the new design criteria was completed in January 2009.

This paper presents the technical considerations of foul air transport in open channel sewers. Design criteria is reviewed and evaluated for air jumper sizing adequacy and configuration based on a comparison of pre-project headspace air flow, vacuum, and pressure conditions to post-project performance. For headspace air jumpers to work adequately, the air jumpers must be designed to reduce headloss for the headspace air flow rate created by drag from the flow of wastewater in the sewer.

In addition to sufficient sizing, air jumpers must also be designed to drain continuously accumulating condensate to the upstream and/or downstream sewer connection structure. Air jumpers subjected to sewer overflow conditions also may accumulate significant grease deposits and must be designed to allow periodic inspection and cleaning. In many of the 16 existing siphon locations reviewed, there was inadequate vertical clearance to retrofit a full-size air jumper meeting capacity, drainage, and cleaning criteria. There were also many horizontal alignment conflicts limiting size and/or location of new air jumpers. Therefore, in some locations, a set of smaller multi-barrel parallel air jumpers, equivalent in air handling capacity to a single larger diameter air jumper, were designed and constructed to achieve adequate capacity. Using a set of parallel pipes for increasing capacity is not a new approach, however, a new approach for utilizing junction air boxes for transition of air jumper size and direction was developed. The air boxes were designed for changing horizontal and vertical direction of air jumpers, while also providing access for air jumper cleaning and condensate drainage. This air jumper manifold and junction box design approach will be presented.

The are significant benefits to avoidance of foul air emissions by applying the recommended air jumper sizing criteria to any existing sewer with hydraulic blockage due to hydraulic jump, debris or grease, or due to an inverted siphon. Omitting air jumpers, or using historic rule-of-thumb recommendations for air jumper sizing, are often not adequate to avoid wastewater collection system emissions and odor complaints.

Keywords: Inverted sewer siphon; air jumper; air transport; depressed sewer; drag; odor control; reduction factor; sewer headspace; vacuum

Document Type: Research Article


Publication date: 2009-01-01

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