Untreated sewage overflowed into Spokane River after Tuesday rain, snowmelt

Untreated sewage and stormwater was released into the Spokane River this week, as some of the system was overwhelmed by weeks of snow and sub-freezing temperatures followed quickly by days of rain and relative warmth.

In some areas of Spokane, sewage and stormwater flow into the same system before traveling to the city’s wastewater treatment plant. During heavy rain or rapid snowmelt, the stormwater runoff flowing into these combined sewers can overwhelm the system, causing overflows into the Spokane River.

Massive underground tanks, some of which can store more than a million gallons, are located throughout the system to help handle some of the additional water. But even this additional capacity is periodically overwhelmed, as it was on Tuesday.

Between 3 a.m. and 1:30 p.m. Tuesday, as rain and warming temperatures melted accumulated snow, overflows were reported at six monitoring stations along the Spokane River.

The combination of raw sewage and stormwater can carry a variety of human bacteria and viruses, as well as potentially hazardous chemicals, oils and other waste. In addition, state and federal regulations limit overflows to one per year per location.

One of the six stations that overflowed Tuesday, located north of the Downriver Golf Course, was also overwhelmed during torrential rains in June, discharging 1.4 million gallons.

It’s not immediately clear how significant the overflow was Tuesday, said Kirstin Davis, communications manager for the city’s Public Works division.

Untreated sewage flowing into Spokane’s waterways is not a new problem, Davis noted, and the issue has improved significantly over the years.

Decades ago, all of Spokane’s sewage and stormwater flowed untreated into the Spokane River and Latah Creek. In the late 1950s, the city built the first treatment plant, but Spokane’s sewer and stormwater systems still flowed through a combined system.

That system often got overwhelmed, leading to hundreds of millions of gallons of combined sewage overflowing into the Spokane River without treatment.

The 1970s marked the beginning of decades of infrastructure improvements in the city, including separating much of the sewer and stormwater systems and building the underground storage basins to help handle overflow. Though combined sewer systems still exist in portions of the city, especially on the South Hill, those upgrades have steadily reduced the untreated sewage being dumped into the river.

When those infrastructure improvements got underway in the early ’70s, an estimated 447 million gallons of mingled sewage and stormwater was discharged in an average year.

In 2006, when over 22 inches of precipitation fell on Spokane during an unusually wet year, 116 million gallons of sewage and stormwater overflowed from the combined system. By 2017, when slightly more precipitation fell, overflow was around 70 million gallons.

The system has continued to improve, including with a $350 million investment as part of Spokane’s 2014 Integrated Clean Water Plan. In 2021, around half as much precipitation fell as in 2006 or 2017, but less than 450,000 gallons overflowed from the system, the lowest amount to date.