Ventilation Dynamics and Pressurization in Deep Tunnels

It is a well-known fact that wastewater collection systems naturally ventilate in response to the internal conditions of flow velocity, depth and sewer diameter. While the effects of natural sewer ventilation are seen throughout most collection systems as odor emissions, ventilation dynamics is a consideration that is often overlooked and not widely understood. An analysis of the Highbury Interceptor was conducted to evaluate the ventilation and odor emissions of the 116 inch diameter tunnel, which functions as a combined sewer and terminates at a triple barrel siphon. This evaluation included a two month field monitoring program in which continuous differential pressure and hydrogen sulfide data were collected, followed by ventilation modeling to definitely determine the cause of high pressure conditions during wet weather events. The analysis was used to develop a comprehensive odor mitigation strategy to control odor emissions along the entire Highbury Interceptor from one centralized location.