Seattle Builds Subway-Sized Tunnel — for Stormwater

A new, $700 million Seattle tunnel with a diameter large enough to fit a single track train is actually designed solely for wastewater, writes Joe Cortright in City Commentary.

As Cortright explains, “The reason for this tunnel—as in many cities in the US—is to deal with periodic sewer overflows when it rains. Seattle has a system of combined storm and sanitary sewers–so stormwater mixes with domestic wastewater, which is a problem during heavy rains.  The system is sized to avoid overflows when its just handling domestic sewage, but the water flows during the rainy season exceed the capacity of the system.”

Cortright notes that half of stormwater comes from parking lots and roadways, “and much of the toxicity of stormwater is from cars and trucks (oil, tire debris, brake dust and precipitated air pollution)” — so transportation is directly responsible for added costs for sewer and stormwater infrastructure, but drivers do not contribute directly to costs. “Instead, the cost of sewage subways gets build to urban households, many of whom don’t even drive.”

According to Cortright, the city’s approach to water pollution is “both inefficient and inequitable: inefficient because we’re not sending any incentives to people to drive less, and inequitable because we’re not asking the people causing much or most of the pollution to pay for the solution.” In this way, “Not asking road users to pay for the cost of the subway built to handle their toxic runoff, and instead loading it on to the bills of households or businesses, makes driving artificially cheap, and city-living artificially expensive.”