Innovative Design Corrects Sewer Siphon Odors

After receiving resident feedback that its sewers were emitting odors, Orange County Sanitation District (OCSD) launched an investigation into the effectiveness of its sewer siphons’ ventilation.

While the Fountain Valley, CA district has a proactive siphon cleaning and maintenance program, the number of odor complaints in the vicinity of siphons indicated they were the problem.

OCSD’s 471-square-mile service area includes 21 cities and three special districts. Its regional transmission system encompasses 475 miles of interceptor and trunk sewer lines. Additionally, its system includes 17 pump stations and two regional wastewater treatment plants that process an average daily flow of 243 millions gallons per day.

The investigation looked at 16 of 87 sewer siphon locations. Six locations did not have an air jumper, and of the 11 sites that did have air jumpers, most were not adequately sized – causing the release of malodorous air.

“The challenge was to develop proper air jumper sizing guidelines without clear industry standards,” explained Steve Deering, the Dudek principal engineer who led the investigation.

OCSD identified the 16 most odorous siphons in need of rehabilitation as part of an overall collection system siphon assessment field study. The field investigations involved wastewater flow, air flow, air vacuum and air pressure monitoring upstream and downstream of each siphon to determine and define the sewer headspace conditions approaching and leaving each siphon.

The field data was analyzed and a rational site-specific siphon air jumper capacity and sizing method was developed. Recommendations for the maximum headloss (pressure drop) allowable, in inches of water, were made for specific air-flow rates and length of air jumpers required for each siphon.

Design drawings for construction of adequately sized air vents/air jumpers for each of the siphons were developed that included new industry methods for multi-barrel extremely shallow construction over existing storm drain culverts.

OCSD now has properly sized siphon air jumpers at its 16 subject sewer siphon locations, which will significantly reduce odor emissions.