Full-Scale Interceptor Drop Structure Ventilation Analysis in Los Angeles Reveals Keys to Odor Release

Several years ago City of Los Angeles (City) engineers identified the buildup of positive differential air pressure in their interceptor system as the primary cause of odor complaints in Central Los Angeles. When the Northeast Interceptor Sewer (NEIS) and East Central Interceptor Sewer (ECIS) both came online by 2005, interim odor scrubbers had been installed at five drop structures along the NEIS and ECIS alignments. The City subsequently recorded more odor complaints when the interim scrubbers were running than when they were turned off, especially along the shallow North Outfall Sewer (NOS) segments that carry flows to the NEIS and ECIS via the drop structures. This raised a question among City officials as to the ultimate need of permanent Air Treatment Facilities (ATFs) at these locations. A study, which is the subject of this paper, was then commissioned by the City to answer this question.