Spokane’s effort to prevent raw sewage from spilling into the river through an aging pipe system is nearing the finish line.
The city is expecting to have all its planned construction of stormwater retention tanks under contract by the end of this month, finishing a process that began with the construction of a 360,000-gallon tank near the Riverside Water Reclamation Facility in 2003.
The tanks hold water during heavy rainfall to prevent it from mingling with sewage. If the pipes are too full, they trigger the release of untreated water into the Spokane River.
An agreement with the Washington Ecology Department requires the city to demonstrate that it is working toward completion of the new stormwater retention system by the end of this year.
Last year, a total of 80 million gallons of untreated sewage entered the river, according to the city’s annual published report of overflow events. Through September of this year, 54 million gallons of untreated water were recorded flowing into the Spokane River.
Three projects, two of them traditional tanks and one a “green solution” that involves burying filtration chambers beneath sidewalks in west Spokane, are slated for approval this month. Construction will begin next year.
Subterranean cells in West Central
Plans to capture stormwater from entering the sewers in West Central include the construction of 250 subterranean sidewalk chambers of various sizes known as “Silva cells.”
The chambers will act as underground “swales,” capturing water during intense rainfall that will then be absorbed into the soil beneath.
“This is the first project that we are actually going to do, holistically, with green solutions,” Kyle Twohig, the city’s engineering services manager, told the Spokane City Council this week.
At the street level, the chambers will appear as planters that will include grass and trees. Adjacent property owners will be asked to mow and maintain the plant life after some neighbors objected to using cement or rock formations in the design, according to city staff.
The work is expected to cost an estimated $3.7 million and will cause intermittent lane closures throughout the western half of the neighborhood during construction.
The city says an additional 60 to 80 trees will be planted in the neighborhood as part of the work, and sidewalks that are not currently handicap-accessible will be upgraded.
Two tanks in Kendall Yards
A pair of tanks, capable of capturing 40,000 combined gallons of stormwater, will be buried at two locations in the rising neighborhood just north of downtown.
The first tank is planned at the doorstep of the Washington Court of Appeals building just off Cedar Street and Summit Parkway. Crews will start the work early in the construction season and hope to finish by the end of May, just in time for the beginning of the summer farmers markets hosted by the neighborhood.
“It’s a 10,000-gallon tank, so it’s not going to take forever to build,” Twohig said.
The second, 30,000-gallon tank will be built at the intersection of Bridge Avenue and Ash Street, near the stairs leading up to West Central from Maple Street. The combined work is expect to cost between $1.3 million and $1.4 million.
Disruptions planned around Peaceful Valley work
Work on a 50,000-gallon stormwater tank near the intersection of Main Avenue and Cedar Street will cut off one of two potential routes into the historic neighborhood.
A pedestrian path will be maintained from downtown on Main Avenue to Peaceful Valley, and the stairs providing access to Riverside Avenue will be reopened. But Spokane Transit Authority service will be affected by the construction.
“We’re going to work with them on a solution during construction,” said Brandon Rapez-Betty, a spokesman for the public transit service. “They are not going to lose service for the duration of that project.”
In addition to the tank, crews will be extending stormwater line piping down Main Avenue and into two planned swales north of Bridge Avenue, near the Spokane River. The work will also include construction of a 10-foot-wide paved trail, which will eventually connect with a planned South Gorge looped trail across the Sandifur Bridge that has been put on hold over a budget dispute in the Washington Legislature.
The Spokane Tribe of Indians will be on hand to observe excavation near Glover Field, following concerns raised in 2013 about the original site of the tank. The area, once used as a field for high school football games and other gatherings, was also a popular gathering spot for the tribe because of its proximity to the falls and fishing.
Total construction cost for the Peaceful Valley work is expected between $3.8 million and $4.3 million.