North Bend’s 50 year-old wastewater treatment plant is the source of complaints about ongoing unpleasant odors, and in the summers, of complaints about murky and foamy discharges into the South Fork of the Snoqualmie River.
City officials have acknowledged the odor problem, and are in the middle of a plan to address it, but the occasional discharges of seemingly untreated water from the plant are more difficult to manage.
Residents like David Willson and Bryan Townley, who reported and photographed an apparent sewage discharge into the South Fork just before 6 p.m. on Sunday, Oct. 16, say it looked and smelled like raw sewage.
“The dirty water, brown and foaming, was pouring out of the spillway which is about 20 yards downstream from the bridge and on the right side of the river facing the downstream direction,” Willson wrote in an e-mail to the Record, describing what he saw that afternoon as he crossed the South Fork. “The left side of the river was crystal clear, stones on the river bed clearly visible. On the right side, there were tufts of foam circulating in an eddy full of brown water with a strong offensive odor.”
Townley, a former treatment plant worker, said he saw a similar discharge of “subpar water” in September, and a third incident some time before then.
North Bend staff, however, are positive that all of the water discharged into the river has been treated, and the weekly tests conducted on Monday showed all discharge water within acceptable ranges for two common pollutants from sewage.
Public Works Director Ron Garrow said the plant might have taken in “too much inflow” during processing that weekend, which “could allow the stuff in the oxidation ditch to get through before it was all settled… but it still gets disinfected.”
Wastewater travels through the treatment plant in channels, at a rate of 500,000 to 750,000 gallons daily. First it is filtered for non-degradable solids, such as toys that are accidentally flushed, and then it goes to the outdoor oxidation ditch, where natural processes break the materials down over days or weeks. From there, it is routed to a clarifier to allow any remaining solids to sink to the bottom of the channel, and disinfected with ultra-violet lights. The water is then discharged into the river, and the solids are collected and dried.
Clogged pipes could cause an overflow, Garrow said, and that would spill raw sewage, but those incidents are rare. The last time it happened was the March 2008 spill that flooded the neighboring Youth Activity Center. In that incident, Garrow noted that all of the sewage spilled onto land, none into the river, and the city was not fined for it.
Odor from the treatment plant is a more common complaint. North Bend contracted with two agencies earlier this year to evaluate the problem, which appear to originate with the drying process of the collected solids, and suggest solutions. Phase 1 of the three-step plan was to replace the two air filters in the drying section of the plant, which will be done every two years.
The North Bend City Council approved the start of Phase 2 at its Nov. 1 meeting. In this phase, equipment for managing the conveyance and drying of the solids will be added onto and upgraded, at an estimated cost of $68,349.
Garrow said these improvements will be evaluated for about a year before the city considers additional steps in Phase 3. Those would include a new enclosure for the drying area and a new ventilation system.
The North Bend City Council meets on the first and third Tuesdays of each month. For agenda information, visit the city’s website, http://ci.north-bend.wa.us.
