Unlikely as it may seem, the massive berms of snow left around Spokane in the wake of storms and a prolonged arctic chill are going to melt.
Overnight lows next week are forecast to remain above freezing, with rain anticipated all week. That means the roughly 10 inches of snow that has piled up over the past few weeks around town will be melting fast, testing stormwater pipes and the massive underground tanks the city has been installing to store combined sewage and stormwater before it’s treated and discharged into the Spokane River.
“We will have overflows,” said Marlene Feist, a spokeswoman for the city’s Public Works Division. “There’s no way to avoid that.”
In 2013, the city approved a plan to build 11 new underground tanks that will bring underground capacity up to 14.3 million gallons before runoff tips the limit and combined sewer and stormwater overflow runs untreated into the river.
Some of those tanks are already online – three massive reservoirs, including the 1 million gallon tank being buried under the Bosch parking lot on the north side of the Monroe Street Bridge. Two other tanks, one near downtown and the other at the intersection of First Avenue and Adams Street, will begin construction this year.
The tanks are designed to bring the city in line with a mandate from the Department of Ecology to limit untreated water flowing into the river at 20 sites to once per year. In the 1970s, that number was closer to 1,000 per year, spilling more than 700 million gallons of untreated water into the river.
Over the past five years, the average amount of untreated water that has entered the river as a result of system overflows has been about 52 million gallons, according to numbers reported to the Ecology Department by the city.
Brook Beeler, a spokeswoman with the Ecology Department, said the agency was more concerned about overflows in the summer months, when warmer temperatures are more conducive to algae blooms and water levels in the Spokane River are lower.
“In the winter, the amount of pollution impact is less, because you have less stuff floating in the water,” Beeler said. The main contaminant of melted snow is deicing material, and the product the city uses contains trace amounts of polychlorinated biphenyls, or PCBs. Other contaminants, like phosphorous, are not as big of a concern in colder months, Beeler said, making a deluge during dry summer months more of a concern than snowmelt in the winter.
To make sure the melting snow finds its way easily into the system and not in ponds on city streets, both the Ecology Department and city are urging residents to clear drains around their homes of ice. Feist said city crews will be out on the streets this week to clear drains, after a four-day effort to plow the entire city following heavier-than-anticipated snowfall last weekend.
Feist said the likelihood of the system being overwhelmed increases with warmer temperatures and rainfall, which can accelerate melting. The National Weather Service in Spokane is warning such conditions will likely move into the area early next week, though river flooding is not anticipated, according to forecasters.
Construction of the stormwater tanks is being funded largely through the sale of so-called “green bonds” secured in partnership between Mayor David Condon’s administration and the City Council in November 2014.
Feist said the tank that has been under construction on Pettet Drive, commonly known as Doomsday Hill, is operational and is being calibrated now to begin to collect stormwater. A tank on Northwest Boulevard that holds 900,000 gallons is also operating. The city also has the ability to drain some of the water in a tank if levels are approaching overflow, as officials did during a particularly heavy rainfall in May.
“We can fill it, drop the level, and fill it some more,” Feist said.
Beeler said the Ecology Department will continue to work with the city on enforcement, understanding the stresses of heavy rain and snowmelt on a system that is under construction.
“The progress that’s been made, has made a significant difference,” Beeler said.
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