Portland's ongoing major sewer reworking -- known colloquially as the Big Pipe project -- may make the Willamette River cleaner, but it may also make the air in certain parts of the city decidedly less pleasant. And so the city's going out to bid for a contractor to design an "odor control" system for the neighbors whose olfactory senses are going to be assaulted. The request for proposals explains:

The Portsmouth Force Main is an element of the Willamette Combined Sewer Overflow (CSO) system that will convey up to 120 million of gallons per day (MGD) of combined sewage from the Swan Island CSO Pump Station (SIPS) to the Columbia Boulevard Wastewater Treatment Plant (CBWTP).

Based on the most recent operating plan, which includes both wet weather and dry weather operation, the new Portsmouth Force Main may generate hydrogen sulfide and emit odors at the discharge end of the pipeline. Swan Island CSO Pump Station design and construction work will include a chemical injection system to suppress sulfide generation in the force main. However, due to intermittent operating scenarios, the discharge of the pipeline cannot be guaranteed to be odor-free. The design and construction of this facility will treat foul air exhausted from the sewer system and protect the neighbors from nuisance odors.

This project provides design (pre-design and final design) of odor control facilities that will be installed at the discharge end of the new Portsmouth Force Main where it connects to the existing Portsmouth Tunnel at what is called the "North Shaft" for the Portsmouth Force Main. The Portsmouth Force Main design provides two exhaust ducts (30-inch and 10-inch) from the North Shaft to a foul air vault at grade that is open to the atmosphere. The Portsmouth Force Main Odor Control Facility will provide design of a ventilation and odor control system to treat the foul air from the force main and the tunnel and will connect to the foul air vault, which will be located at 6825 N. Willamette Boulevard.