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As part of the Clean Water Project, the Metropolitan District (MDC) of Hartford, Connecticut upgraded existing combined sewer systems by installing storage tunnels to prevent raw sewage from overflowing into the Connecticut River. Mulitple ventilation shafts were located along a 2+ mile long storm water overflow tunnel. The tunnel included odor control systems located at each of the ventilation shafts and droptubes to handle the emittance of foul air from the tunnel.

The study was performed to predict the quantity of foul air exiting through each of the droptubes and ventilation shafts during two scenarios: a buoyant condition where colder ambient air would create an upflow from the tunnel, and a storm condition where the incoming water would displace the foul air. The results were used to properly size the odor control systems.

Work Performed Two time-dependant Computational Fluid Dynamic (CFD) models of the planned tunnel system were created. The models used historical temperature and storm data in the surrounding area of each droptube and ventilation shaft to define the test conditions for each simulation. The buoyancy model simulated the time-lapsed effect of the warm foul air rising out of the tunnel and being displaced by the colder ambient air. The storm model simulated the duration of an extreme storm case with water entering each droptube based on the local water data for that area. Each model provided the flow rate versus time of foul air exhausting (or ambient air drawn in) at the droptubes and ventilation shafts.

The storm model provided additional insight to the flowing water patterns within the tunnel during a storm event , as well.