Sewer plant overflow highlights problems of aging wastewater infrastructure

Published 2:06 pm Tuesday, May 17, 2016

A temporary stop in the North Bend wastewater treatment plant’s processing pipeline a week ago led to a minor overflow of sewage. The leak, said city Public Works Director Mark Rigos was “very minor,” and was cleaned up immediately.

The spill reportedly occurred Sunday, May 8, when a worker at the plant turned off a pump to do some maintenance work. The 62-year-old plant needs regular maintenance because it operates basically around the clock, Rigos said.

A centrifuge in the plant continued operating, which caused a small amount of untreated wastewater to overflow a weir and spill onto the ground.

“It was basically just a little bit of foam that was overtopping the weir,” Rigos said. He estimated the affected area that the wastewater touched was five feet by five feet or less. “It looked kind of bad, but the reality is there was very little liquid with that foam.”

Plant workers immediately cleaned the area, spraying the wastewater into a catch basin that fed back into the treatment plant.

“It was hundreds of feet away from the river,” Rigos added.

Because this overflow was so minor, it was not reported to the State Department of Ecology, which permits the plant. There have been reportable spills in the recent past, though. An overflow Dec. 8 was caused by high flows — a record 4 million gallons through the plant, Rigos said — caused by heavy rain and a high water table from the previous four weeks of flooding in the area.

North Bend is permitted to process 2.5 million gallons of wastewater per day, and usually, the plant’s output is much lower than the permitted amount. Rigos said the plant will also be able to absorb the impact of the estimated 1,100 new homes now in some stage of permitting or development in the city, too.

“The population now is about 6,700… we could be at 10,000 people in five years,” he said. “Our treatment plant is fine for that growth. What our plant is not fine for is 12,000 people right now.”

For the past two years, the city has been steadily updating elements of the wastewater treatment plant, to increase capacity: A new outlet structure, gate and piping for the plant’s oxidation ditch in 2014; updates to the aeration system and a conveyance system for sludge disposal in 2015; and coming up this summer, a new UV disinfection unit.

To fund these updates, as well as ongoing repairs, Rigos said North Bend will have to increase its sewer rate and general facilities charges (GFC, a one-time fee charged for new connections to the sewer system). Rate increases have been proposed to the city’s Public Health and Safety Committee and the committee is expected to forward the recommendations to the North Bend City Council in mid-June.

Rigos noted that, in keeping with the city council’s goal that “growth pays for growth,” the GFC funds will be directed to increased capacity projects such as the new UV disinfection system, while the sewer rate funds will be directed to ongoing maintenance.

As proposed, the sewer rate change would maintain the base rate for sewers, about $75 per month for a single family home, but increase the variable rate that changes with the amount of water used.

The North Bend City Council will schedule a public hearing on the proposed rate changes before voting on the issue.