It’s no surprise that the smell is the worst at “solids” processing. But the good news for workers at the Redondo wastewater treatment plant is that it gets better from there.

Wastewater from the sinks, showers, toilets and dishwashers of about 46,000 people in Des Moines and northeastern Federal Way flows to this facility, which is tucked away in the woods above Cold Creek, just 800 feet away from the waters of Poverty Bay.

The pipes — around 114 miles of them — from those thousands of homes and businesses all eventually lead to the facility, where the flow is strained, disinfected and released into Poverty Bay. The vast majority of the time, that process goes smoothly.

But some heavy rainstorms throw so much extra water in the mix that the plant can’t keep up and must spill some not-fully-treated water over. As a result of those roughly once-a-year events, the state health department is downgrading commercial shellfishing in the area around Cold Creek from “conditionally approved” to “prohibited,” according to state Department of Health Shellfish Growing Area Section Manager Scott Berbells.

The system is built to handle wastewater, not the rain from storm water, which infiltrates the system and unnecessarily adds to the treatment plant’s load when it rains. That storm water is called “infiltration and inflow,” aka “I/I,” and it’s the prime culprit of those spills, Lakehaven Water and Sewer District General Manager John Bowman said.

“The overflow occurs because of off-site problems,” Bowman said. “The process here can treat the daily stuff that we normally get.”

The plant is built to handle a peak monthly average flow of 5.6 million gallons per day (MGD), though it can contain much more if needed. Summer flow rates average around 2 million gallons per month, while the facility can average around 4 or 5 million gallons during the winter. But during winter rainstorm events, the plant can temporarily be slammed with flows well in excess of 10 million gallons per day.

Currently, only geoducks are commercially harvested in the Poverty Bay area, Berbells said. The burrowing clams are harvested at the subtidal zone, or the part of the sea just beyond the shore that is always underwater. There is no public shellfishing in this area, except at Dash Point State Park. Just like cutting trees or farming corn, only some of the geoduck tracts in the bay are currently ripe for harvest. Other tracts in the bay were harvested recently and will need years to recover, and if pollution isn’t curbed, the viability of those tracts could be compromised for decades.

In 2016, the state Department of Health (DOH) downgraded about 125 acres of the bay’s nearly 1,000-acre commercial shellfish growing area from “approved” to “conditionally” approved, based on higher rates of fecal bacteria detected during the summer. Now a large section of the area — centered on Cold Creek — is about to be downgraded to “prohibited” because major rainstorm events from the Redondo plant create a risk of high bacteria loads in the winter, Berbells said.

Now Lakehaven is looking at ways to prepare for those rainstorm events and reduce the amount the plant has to spill. But property owners can also take steps to keep their waste water lines clear — and help clean up Poverty Bay in the process.

Photos by Alex Bruell/Sound Publishing This outflow channel is the last line of defense at the Redondo Treatment Plant to keep in wastewater. During severe rain events, stormwater adds to the load so much that the wastewater spills into this channel. What water goes over the wall can reach the Cold Creek from here. For the vast majority of the time, this channel is dry.

How it works

The Redondo Treatment Plant is one of two in the Lakehaven district. The Lakota plant processes waste from the west and south part of Federal Way, while the Redondo plant captures wastewater from the north and east.

Bowman and Lakehaven operations supervisor Brian Richardson took the Mirror on a tour of the Redondo facility in August to show how wastewater becomes ocean water.

The process is intuitive: Waste water flows in first at the headworks, the highest point of the Redondo facility. Each step of the process, generally, is a little lower than the last, allowing gravity to do much of the work.

Toilet paper, gravel and other debris are sorted out first at solids processing. So-called “flushable” wet wipes are also dealt with here — like other debris, they have to be sorted out when they reach the plant.

Next, two primary clarifier rooms separate the remaining solids from the wastewater. Large blades stir and scrape the sludge of heavier materials away from the rest of the wastewater to where it can be collected.

The clarified water from those rooms are pumped into biotowers, where bacteria, housed in plastic filters that look almost like LEGOs, feast on the wastewater and treat it further. The sludge, meanwhile, is broken down over several weeks by “digester” tanks and then dried out at the solids handling building. Eventually, it’s shipped off and used as fertilizer.

Meanwhile, the waste water streams through two more secondary clarifiers and then heads to filtering and disinfection. The plant bathes the water in green ultraviolet light, which kills pathogens by breaking apart their DNA. When too much water gums up the system from heavy rain, it pools in this area near the very end of the process.

Outside the disinfecting room, an outflow channel a little less than a foot deep stores that excess water and directs it back into the facility. But when it’s too much for the system to bear, the “effluent” mix of clarified wastewater and storm water spills over the channel and onto a hillside by the plant, where some of it reaches Cold Creek and pours into the ocean.

A rainstorm on Feb. 28, 2022, caused roughly 200,000 to 400,000 gallons of effluent to spill over, according to a recent report. The extra foot or so of that outflow channel probably prevents another million gallons or so from spilling over during those events, Bowman said.

The water that spills that way is already near the end of the treatment process, but it’s undertreated and not yet disinfected. It still contains some fecal coliform bacteria, which in large numbers can sicken humans and upset aquatic environments.

Even when it’s not flooding the disinfection room, that storm water is a nuisance to waste water operators. It dilutes the whole operation and makes it harder to scrub the waste water clean.

According to an April 2022 report by the Department of Health: “Reviews of discharge monitoring reports have shown that significant I/I (“infiltration and inflow”) has caused periodic treatment efficiency problems … during high rainfall events.”

These green UV lights at the treatment plant help disinfect the wastewater near the end of its treatment process.

What can be done

Building the outflow channel any deeper would require serious, expensive reinforcing of the facility, and could cause water to start flowing out of other buildings, Bowman said.

“We’ve got about as much as we can contain,” Bowman said.

And it would only be a band-aid solution, because the real task is keeping the storm water out of the system all together.

But identifying and fixing the I/I (“infiltration and inflow”) problem is expensive, so they’re focused on fixing the worst offenders, Bowman said. Since 2016, Lakehaven has completed four repair projects, lining around 4.2 miles of sewer main, 250 side sewer connections, 86 side sewers from sewer mains to houses and 86 manholes, Bowman said.

This spring, Lakehaven will also resume running cameras down sewage pipes to find the worst leaks, a process Bowman described as similar to piloting a remote control car with a camera attached.

Lakehaven also has a consultant evaluating a more ambitious solution to the problem: Building miles of new piping so that during the rainstorms, some of the Redondo flow could reroute to the Lakota plant, which has far more capacity and could help shoulder the burden during high-flow events.

It wouldn’t solve the I/I problem, but it would could help avoid overflow events, Bowman said. The consultant is still evaluating the concept and nothing is set in stone.

Homeowners have a role to play too. Maintaining the side sewers on your own property is generally your responsibility, assuming you don’t use a septic system. Groundwater can seep into those pipes, especially if they’re old and made of concrete. And those with water problems on their property, people should not try to pump excess storm water to their sewer line, Bowman said: “No vagrant water should be routed to the sewer system.”

Learn more

Lakehaven can guide you through the process of repairing, adding or inspecting a sewer connection, including issuing a no-fee permit and recommending licensed and bonded contractors, Bowman said.

For more information, call the utility’s Development Engineering Section at 253-945-1580 or 253-945-1581, or visit www.lakehaven.org.