King County Wastewater Treatment Division employees responded Friday afternoon to stop a sewage overflow into Ravenna Creek, begin cleanup of the affected area and investigate its cause.
An estimated 8 million gallons of sewage overflowed from a stormwater pipe into the creek over a 10-day period. City of Seattle utility crews alerted the county to the overflow after their monitoring equipment detected unusually high stormwater flow volumes despite mild rainfall.
County employees discovered that sewage had been mistakenly diverted into a City of Seattle stormwater pipe instead of the Laurelhurst Trunk during a county project to repair a regulator gate in the Lake City Tunnel.
A number of sewer separation and diversion projects in the Ravenna area over the past several years could have made it difficult for utility crews to determine the exact location of the sewer trunk line. The county will conduct a thorough investigation over the next several weeks.
The overflow has primarily impacted a mile-long stretch of Ravenna Creek from Northeast 45th Street near Mountlake Boulevard to the Union Bay Slough.
To protect public health, the county has posted public areas as closed, took water samples and notified health and regulatory agencies about the overflow. Because of the overflow volume, the county’s environmental lab will also conduct water quality testing to determine potential impacts to Union Bay and the Lake Washington Ship Canal.
