The downpour that slammed Spokane in mid-May, flooding downtown streets and basements during a nightmare Thursday evening commute, caused more than 16 million gallons of untreated runoff to spill into the Spokane River.
And that’s just the amount the city knows about, according to its required monthly report on the city’s combined sewer and stormwater system to the Department of Ecology for May. Several sensors were damaged or unreadable due to the torrential stream of water flowing through city pipes, causing a lack of data at several locations where runoff flows directly into the river when the municipal system becomes inundated. The numbers from those tanks are likely even higher than what is included in the report.
Marlene Feist, city spokeswoman, said the unusual intensity of the rainfall that evening coupled with debris jamming street drains led to the overflows, which were necessary to avoid damage to the city’s main collector pipe that runs wastewater to the treatment plant northwest of town.
“It’s all about protecting the interceptor. An overflow from one of the tanks is much better than risking the integrity of the interceptor,” Feist said.
But Spokane River advocates say the event could show the system’s inadequacy to deal with larger storms that will become more common due to the effects of climate change.
“Hopefully we haven’t built a freeway designed for last year’s traffic,” said Jerry White Jr., Spokane Riverkeeper.
The city has invested $200 million in so-called green bonds toward the construction of subterranean tanks of varying sizes. They are supposed to capture fast moving water during heavy rains and hold it until the pipes can carry additional runoff. If too much is released into the city’s combined system, that stormwater coming off the streets trips outfalls in the pipe and is combined with untreated sewage. That runoff then spills into the river before reaching the Riverside Park Water Reclamation Facility.
The tank system under construction was downsized based upon new calculations published in 2013. Those calculations looked at rainfall totals in Spokane between 1993 and 2013, and did not include any adjustments based on potential changes in precipitation amounts due to climate change.
Spokane separated its sewer and stormwater systems on the much of the North Side in the 1980s and ’90s, reducing its overflow events into the river by about 75 percent, according to city records. In 2018, the city reported the lowest amount of untreated water flowing into the river since 2011.
In all last year, 38 million gallons of untreated water flowed into the river, according to the city’s published data. May’s total was about half that, at 17.5 million gallons, the most untreated water that has spilled out of the city’s system in a single month since February 2017. Melting snow that month caused a rash of potholes on Spokane’s streets at the same time 28 million gallons of untreated water spilled into the river.
While the majority of the untreated water that entered the river during May’s storm came from pipes connected to massive chambers downtown and in Liberty Park that had not yet become operational by the time the rains arrived, the deluge also washed out two new pieces of infrastructure that have been built since the city adopted a new stormwater plan in 2013. Those two operational tanks near the West Central Neighborhood combined to spill more than 3.6 million gallons of untreated runoff into the river over a period of hours that didn’t end until the following day.
Those tanks – a 900,000-gallon chamber built at Northwest Boulevard and Kiernan Avenue at a cost of about $9 million and a 690,000-gallon tank at the top of Doomsday Hill costing $7.6 million – were also located near some of the heaviest rain totals reported that afternoon, according to National Weather Service data. A spotter near the Spokane County Courthouse in the West Central Neighborhood reported 0.9 of an inch of rain during a 20-minute period beginning at 4:45 p.m. May 16, said Matt Fugazzi, a meteorologist with the National Weather Service in Spokane.
“That’s highly impressive, but it’s not unusual,” Fugazzi said. “It’s not unheard of for a summer-type thunderstorm.”
Still, that amount is a little more than half of the expected rainfall total in Spokane for the entire month of May, based on historical averages, and it all fell in less than a half-hour. Feist said the city’s infrastructure wasn’t designed for that type of storm, but could handle such rainfall if it fell in more predictable intensities throughout the day.
“Our system isn’t really built for an inch in 20 minutes,” Feist said. “There’s no way to build a system that could. We couldn’t pay for that, and it would take too much space.”
The Ecology Department, responsible for reviewing the city’s compliance with permits allowing the discharges into the river, also doesn’t believe the May rainfall was a reasonable test of the city’s stormwater system capacity, said Ryan Lancaster, a spokesman for the department, in an email.
“The system should be judged on the typical, not an abnormally intense storm,” Lancaster wrote. “If an event like we experienced in May were to become the norm, then the city would be required to identify and implement a system that would be protective of the river.”
Rachael Pascal Osborn, a water rights attorney who’s worked with the local chapter of the Sierra Club and the Center for Environmental Law & Policy, said the city and state are using the wrong standard to judge the sufficiency of the system. Spokane is allowed one overflow per outfall site, per year, on a rolling 20-year average, based on its permit for discharge with the Department of Ecology. That’s too low of a bar, Osborn argues, and may not be in compliance with the requirements of federal law.
“Nobody’s challenged it to date,” Osborn noted. “But because of that standard, we said we’ll design our tanks so we have overflows, instead of designing them to prevent overflows. This is exactly what we get because of that.”
Each tank is assessed independently of each other, Lancaster said. Compliance with the permits allowing the discharges is evaluated each September when the city of Spokane releases a progress report containing its work toward reducing overflows.
Osborn said she found the recent overflows particularly troubling given what she saw as other perceived threats to the health of the river, including several dischargers seeking a variance from the Ecology Department to avoid a new, scientifically strict standard for polychlorinated biphenyls (PCBs) and an overturning of the department’s rule on summer flows on the river.
Construction crews are completing work now on the last two stormwater tanks to be completed in town, as well as improvements at the wastewater plant that will increase filtration of pollutants including PCBs. The tank behind the downtown library, as well as two storage facilities in the East Central Neighborhood off Sprague Avenue, are scheduled for completion this fall. Work at the plant is scheduled to be completed in 2021.
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