After Centralia experienced its worst flood in more than a decade, a stinky situation arose.
As rain and flood waters from China Creek inundated city streets, it also leaked into the sewer main, causing overflows in lower elevations of the city’s systems. At about 10 different locations, an estimated 608,140 gallons of diluted sewer water overflowed into streets and streams — in some areas for more than a week.
Despite that large figure, city and state experts say the mix of snowmelt, sewer cleanouts, flood water, stormwater and groundwater diluted the sewage, lessening the environmental blow.
"It really is diluted. It's kind of nature's way of taking care of treatment. Now, do we want sewage overflow? No," said City of Centralia Public Works Director Kim Ashmore, estimating the stormwater in the sanitary sewer overflow event made up about 60 to 80% of the murky mixture.
Colleen Keltz, a water quality spokesperson with Washington state Department of Ecology, said the long term impacts of the recent sanitary sewer overflow on China Creek are likely very minimal, if any are observed at all.
“It’s not the same as having a straight sewage spill, and we’re seeing the water systems move so fast that estimating what a potential impact in a certain area can be difficult,” Keltz said.
Still, cities, states, counties and businesses try their best to avoid sanitary sewer overflows — defined by the federal Environmental Protection Agency as a “release of untreated or partially treated sewage from a municipal sanitary sewer” — in the first place, though that’s easier said than done in a place that sees so much destructive flooding.
Sanitary sewer overflows and sewage can carry dangerous bacteria, viruses, parasitic organisms and other nasty microorganisms, in addition to oils and toxic chemicals, according to the EPA.
Ashmore said he and his staff have been working diligently over the past three weeks to identify, record and clean up sanitary sewer overflows throughout the city.
He recently finalized a staff report with estimates that was sent to the Washington state Department of Health, Ecology, and Lewis County, among other agencies and governing bodies.
He detailed those findings this week to The Chronicle: 10 locations were identified as having experienced sanitary sewer overflows over an eight-day period between Jan. 6 and Jan. 14.
The smallest overflow spanned for four days, releasing about 7,650 gallons at a location along Mellen Street. The largest overflow — which occurred for nine days at 1325 Lakeshore Drive, near the Lakeview Inn — spewed about 242,320 gallons, some likely into nearby Plummer Lake and China Creek near its confluence with the Chehalis River.
Ashmore said these gallon estimates are based on a rate of discharge per minute at each location. Comparable estimates to the most-recent 2007 flood were not immediately available.
“When we have flood events like this, sanitary sewer overflows happen. It’s something we’ve dealt with for decades. We have tried to spend money almost every year — the last couple summers, we spent almost a million dollars per year to tighten up sewer systems,” Ashmore said.
“If you’ve got pipes that are in some cases 20 feet deep, and if the ground water table is 5 or 6 feet deep, that amount of groundwater is above that pipe with that pressure” and can leak, he added.
Residents along a section of Hemlock Street were among the most vocally irate when a manhole at the end of their street began overflowing, spewing overflow into nearby China Creek. James Miller, 64, said he and his neighbors experienced a foul smell outside for multiple days.
Ashmore estimates that section of sewer leaked about 82,640 gallons into China Creek over about a week. But that’s a small impact, he said, compared to the 52 million gallons of sewage and stormwater that was feeding directly into the city’s wastewater treatment facility.
Also, China Creek at its peak had about 448,000 gallons of water flowing through it per second, Ashmore said, which is large compared to the estimated 1 to 2 gallons of sewer overflow leaking into it at any given location.
“Is there an impact? Yes, there’s a small impact. But the impacts are much smaller than if there was 200,000 gallons of raw sewage going straight into the creek when it’s dry,” Ashmore said.
The problem was also likely made worse by households unscrewing their cleanout pipes to allow water in their yards to drain. That flow goes straight into the city’s sewer system.
“We do not want people to do that,” Ashmore said, adding later: “We’re not here to treat groundwater, or rainwater or snow. We’re here to treat sewage.”
Contrary to what was previously reported in The Chronicle, the city’s wastewater treatment facility is not nearing the end of its useful life, Ashmore said. In fact, it’s currently undergoing phase 1 upgrades to add to its capacity. The city is going on 18 years with its current facility, and it still has many years left.
During this most recent flood, more than triple the regular daily amount of sewage was being pumped to the facility — mostly due to stormwater and flood runoff.
“These extreme weather events are really tough. Communities that have the best laid plans can still have issues when they have an extreme weather event,” Keltz said.
Ecology doesn’t currently have any data on the impact of flood-caused overflows and their impacts on aquatic species and creek habitat.
