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Sweet Home wastewater treatment plant loses biological life in basin

By Benny Westcott
Of The New Era/Lebanon Local

On Tuesday, Aug. 9, the Sweet Home wastewater treatment plant experienced an increase of approximately double its usual flow of 700 gallons per minute.

For three to four hours that day, its influent level was at 1,400 GPM. Then, three or four days later, the plant lost nearly all biological life in its aeration basin.

“The suspicion is that something was in that flow that was abnormal that killed the biology of the treatment facility,” Utilities Manager Steven Haney said. “It didn’t kill it initially. It’s kind of like if you take a poison: It may take you three days to die. Nothing happened when that influx happened. We’re guessing that the influx was the cause, but we really don’t know.”

Biological life in the aeration basin breaks down human feces and the pathogens, and bacteria that come with it, “into organics that are safe to discharge into the river and dispose of through our solids management program,” Haney explained.

According to Haney, biological life die-offs have happened in the past as a result of mechanical failures, but he can’t recall one occurring from an event like this.

“We’ve had other similar events where something came into the treatment facility that was unidentified, but this is the first one that killed all of our biology,” he said. “It’s not a unique experience, but it’s the first experience that what they were doing had a detrimental effect.”

The aeration basin has yet to return to normal biological levels.

“We’re still struggling, but it’s recovering,” Haney said. “Sometimes it might be two months after a die-off before you fully recover.”

Signs announcing raw sewage have been posted at the Ames Creek boat ramp directly upstream from the plant’s discharge. Haney described the boat ramp to the Pleasant Valley Bridge as the “heavily affected area” of the South Santiam River.

“We’re hoping the public will know from those signs that it’s a poor idea to swim or go fishing right there,” he said. “The Oregon Health Authority and [Department of Environmental Quality] were well-aware of this occurrence. They were notified. There were follow-up questions and conversations. They did not ask for Waterloo to be posted, and they also did not post a public-health advisory. Given that information, I would say the danger was isolated essentially to our outfall area.”

In general, he added, “Our outfall flow is so minor in volume compared to the size of the South Santiam that it dilutes out to almost nothing. We’re taking samples upstream and downstream, and those are showing favorably.”

City staff conducted initial sampling when the plant became odorous, and tests revealed bacteria exceeding the permitted level of 406 MPN, or most probable number, on E. coli.

At that point, staff began feeding freeze-dried bacteria into the aeration basin, then continued to monitor and take corrective measures to bring the plant back into compliance, working with the Oregon DEQ and local partners. Haney said the plant’s E. coli output is now within DEQ’s accepted range.

The wastewater treatment plant was built in the 1940s, then rehabbed in the 1970s and 1990s. Public Works Director Greg Springman noted that current upgrades through the Mahler Water Reclamation Facility Improvements Project should help staff become aware of unusual flow events sooner.

“Because of the age of this plant, it doesn’t have the ability to alarm us when pH changes or flows change,” he said. “The new plant’s going to have a lot of that instrumentation. We are looking to purchase some sampling equipment and also introduce some sort of pH probe that would allow us to monitor on a more continuous basis.”

He added that with the new system, staff could have continuous reads on pH and electrical conductivity and see an increase in salts in the waste stream.

“There are things that we’ll have in the new plant where if we set parameters through our computer and get outside a certain range, it will alarm staff,” he said. “We do not have that type of technology in this old plant.

With new equipment, he continued, “We would have had the control mechanisms in the new plant to see the flow spike, and we could set parameters outside of the normal flow so we could set an alarm.”

New technology or not, Springman emphasized that the public should take care in considering what they flush.

“The lesson here is that it’s not good to dump large quantities of whatever it is, or even concentrated quantities, into the sewer system without permission, because things like this could happen,” he said. “People need to be cognizant of how they’re disposing of liquids in concentration or large volumes, because it can harm the community sewer system.”

Haney echoed that sentiment.

“The sanitary system is only designed for human waste. It’s not designed for any type of chemical disposal,” he said.