Optimization of Air Flow in a Deep Tunnel System for the City of Los Angeles

This paper discusses the development of a unique sewer tunnel ventilation strategy for a proposed City of Los Angeles wastewater project in the northern part of the City's service area.Air accumulation in sewer tunnels can be a major issue due to high air flows created both in the sewer pipe and in drop structures feeding it. High air flows have many negative impacts, including limiting the liquid flow, accumulating odorous air that requires exhaust and treatment using air treatment facilities at multiple locations, and in extreme cases causing high-pressure air pockets that can release and cause structural damage due to pressure alone.The design team developed methods to reduce those negative impacts by limiting the volume of air entering and conveyed in the tunnel. For a sewer tunnel of this size this project is believed to be one of very few to use a combination of two of these methods: a submerged drop shaft and a varying tunnel diameter. The paper also discusses alternative treatment technologies for exhaust air.