‘Big-box stores underground’

The city of Spokane’s current strategy for reducing sewage flowing into the Spokane River centers on building huge underground tanks. Those tanks hold the storm water and sewage mixture that overflows during big storms or when snow is rapidly melting.

And they are about to get big. City sewage officials compare tanks that will be built in the next few years to “big-box stores underground.”

The advantage to the tank solution is that all the sewage eventually travels to the wastewater plant and is treated. Currently, the city’s plant scrubs about 90 percent of many contaminants found in stormwater, such as PCBs. Other state requirements will force the city to significantly improve that treatment in the next decade.

But while the tanks are effective, they’re expensive. Even the newer, cheaper plan calls for the construction of tanks, and they will be far bigger than what the city already has in the ground.

A tank installed near the confluence of Spokane River and Latah Creek at High Bridge Park about seven years ago, for instance, holds 200,000 gallons.

That compares with two tanks the city plans to start building next year: a 1 million-gallon tank on city land near 20th Avenue and Ray Street and a 2 million-gallon tank at Underhill Park. In the next couple of years, the city will start work on a tank that could hold as many as 5 million gallons on land that used to be part of the Playfair horse track in the East Central neighborhood.

Sometime before 2018, city officials say they plan to build a couple more large tanks, likely in the Peaceful Valley neighborhood. One of those could be as large as 7 million gallons.

The EPA’s new flexibility that has allowed the city to diverge from plans to build tanks to stop the flow from all of its combined sewage isn’t expected to affect the city’s other major wastewater expense required as a result of environmental regulations. The city, other governments that treat sewage and industries that discharge into the Spokane River are required to improve treatment, largely to decrease the amount of phosphorus in the river.

Grant Pfeifer, of the state Department of Ecology, said the EPA’s flexibility rules don’t apply to industrial polluters, and he expects little impact on plans to improve treatment significantly. The city is testing several technologies to better clean discharged sewage.

Jonathan Brunt