Stormwater Management in Western Washington State
A common purpose runs through many, likely most, stormwater projects in the greater Seattle area and other western Washington cities, certainly in the projects profiled in this story.
Their shared goal is to improve and protect water quality in one of the region’s natural treasures:
Puget Sound. One of those cities is Bellevue.
Challenges to managing stormwater in Bellevue include “keeping up with our NPDES permit’s regulations while juggling competing regulations from Fish and Wildlife, the land-use folks, and other agencies. Then there are competing interests from the community, developers, the public at large—juggling all of these,” says Don McQuilliams, operations manager, Regulatory Compliance and Surface Water, in the city’s Utilities Department.
Bellevue is built on a ridge. Other challenges to managing stormwater there are the hilly terrain and glacial soils that don’t infiltrate well.
McQuilliams notes, “We get a lot of rain, but not real intense rain. But lately, in the past several years, we’ve been seeing intense rain storms, particularly in summer.”
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These storms, he says, tend to overload the stormwater system. “The water comes to the surface and it causes flooding. Our system was built to handle our usual [much less intense] storm. It was not built for an intense storm.”
Reflecting on how stormwater controls and systems were set up in Bellevue, McQuilliams notes that stormwater officials in the 1970s “were very future-focused. They built regional detention ponds that can hold water and release it slowly. We can hold a week’s worth at normal intensity and amount.”
Bellevue can lay claim to having either the first or second stormwater utility in the entire US. It was established in 1974.
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How did a small city—albeit in a region with a lot of rain—manage to get a stormwater utility in place when virtually none of the general public and few city officials had ever heard of one, let alone were convinced of its value?
How did Bellevue succeed when many other cities struggled for years to establish stormwater utilities? What made Bellevue’s citizens and elected officials agree to vote for the legislation that would require them to pay more for storm sewer services?
McQuilliams thinks Bellevue’s rapid growth is a factor. “Stormwater was pushed to streams, and flows became flashy. Then areas near streams started flooding. Washington was already on the environmental forefront.”
The environmentally aware residents and groups soon realized that the flooding was increasing, not decreasing. They knew that stormwater had to be managed sooner rather than later.
Western Washington has another environmental concern that is a close second to protecting Puget Sound: improving water quality to protect, and bring back, salmon.
McQuilliams is particularly proud of a stormwater project that resulted in improved habitat for fish. He says, “We replaced an old CMP [corrugated metal pipe] 48-inch culvert with a bridge 35 feet in width on Coal Creek. Prior to the replacement, we were seeing almost no salmon there. Now we’re seeing salmon.”
A low impact development (LID) stormwater project in Bellevue is the retrofit of a parking lot for Downtown Park with a water-quality vault and filter. Now runoff flowing to Lake Washington is treated to remove pollutants. Also downtown is a flood reduction project to reduce untreated overflow going into Lake Washington. A pipeline that used to zig and zag and allowed overflows was replaced. A new 24-inch overflow pipe was laid underneath the street for several hundred yards.
“We try where we can to put in LID, such as the raised planters on the streets downtown. The downspouts on the buildings come into the planters and water slowly percolates into the soil. They hold water [slowing runoff speed and volume] during storms. During normal rains we’re seeing a big reduction in runoff,” says McQuilliams.
He sees more acceptance of using LID or green infrastructure, especially bioretention. “Our permit in Washington requires that we address LID as the preferred method of stormwater management. We’ve been promoting it for years; now developers have to look at it.”
He says that another stormwater management strategy in Bellevue is working with officials in nearby communities. “We take a regional approach, most certainly.”
Bellevue has been growing rapidly in population. One reason is the city’s proximity to Seattle. Another is its pleasant living conditions. “Bellevue is unique in how its park system was put in. You can walk or bike around the entire city through the parks,” notes McQuilliams.
Another factor spurring growth in Bellevue is the construction of a light rail system. It will run up the Bel-Red (Bellevue to Redmond) corridor to Microsoft’s headquarters. Unlike some other cities that are experiencing increased urbanization, Bellevue has an unusual opportunity with the railroad and surrounding future residential and commercial development. Because this is all happening in an abandoned urbanized industrial area, Bellevue can improve things with development instead of allowing the area to become more crowded.
McQuilliams says that stormwater features will be added as the railroad line is installed. There are “lots of stormwater permit applications already.” In addition, the City is “already identifying in the master plan ways to rebuild and tie together by stormwater projects.”
When older streets in Bellevue are remodeled, he says, “The transportation department does the best they can to put in bioretention, to make it an LID system. Sometimes they seal off the old system, leave it in place, and build a new one.”
McQuilliams says that pervious pavement and porous asphalt have been installed on many sidewalks and parking lots, mostly private. “Most of our [city] sidewalks are porous concrete, with a rock garden underneath. The flow under the sidewalk goes into the storm system.”
He adds that while the sidewalks lessen runoff, they cause a different problem: moss. “It grows everywhere in Seattle and has strong roots. We can’t use chemicals on moss, so we let it grow and then knock it off with a stiff brush. It’s a danger to pedestrians who might slip and fall.”
Managing stormwater in a fast-growing city always brings challenges. Now McQuilliams has a new challenge: catch basins.
“We had an increase from our catch basin inspection requirement of once during the permit term [once in five years]. Starting in August 2017, we have to inspect each catch basin on average 2.5 times within the five years. That’s going from 5,000 catch basin inspections to 12,500 each year.”
Swale on Yale
Besides a catchy nickname, Seattle’s Swale on Yale stormwater project has another formal name: the Capitol Hill Water Quality project. The project is situated just north of downtown Seattle in an urban neighborhood of historic homes that attracts many visitors.
The primary goal of the Swale on Yale project is to protect and improve the quality of water in Puget Sound. This goal is being achieved by improving the quality of stormwater that flows in from the South Lake Union neighborhood.
Removing pollutants from the runoff required a joint project with creative design and engineering behind it. KPG provided landscape architecture services and KPPF did the engineering work.
The project is a collaborative effort of Seattle Public Utilities (SPU), Seattle City Light, and the Seattle Department of Transportation. Vulcan Realty, a private developer, is also a partner. Total cost of the project is $9.8 million. Vulcan Realty donated $1.3 million.
The project’s innovative features are especially notable in its urban setting with limited space. Its key elements are four block-long biofiltration swales installed between the street and sidewalk. The swales are each approximately 300 feet in length, minus about 30 feet at each end for utility installations. They vary in width from 10.5 to 16.5 feet. Two swales are on Yale Avenue North and two are on Pontius Avenue North.
“It’s a pretty special project. Vulcan gave up two sides of the street for parking. They realized that they needed to help with the stormwater,” says Paul Fuesel, RLA, principal with KPG.
Because Vulcan gave up its parking easement, there was room for a wide walk between the swales and buildings. The realty firm has a history of incorporating green infrastructure into its projects.
Fuesel says the first two swales are working well. “The city is heavily monitoring them,” he notes.
The first two swales were completed in 2013. Construction on the second two will start near the end of this year.
Densely planted sedges and rushes in the swales remove heavy metals and other pollutants in the incoming runoff. Plants used include Carex dipsacea (autumn sedge), Carex elata (Bowles’ golden sedge), Carex obnupta (slough sedge), Juncus patens (elk blue or California blue rush), and Juncus effuses (Quartz Creek rush).
This stormwater project has three main parts that work to move the runoff through it. When the entire project is finished, about 2,000 feet of new pipes will convey the untreated stormwater into an diversion vault. The pipes range from 12 to 18 inches in diameter.
The underground vault—a 96-inch precast concrete structure—sends the stormwater runoff into the swales. It was placed as a saddle manhole over the top of the existing pipe. The base was cast in place. The diversion structure has a baffle wall to divert the low flows to the swale system. It allows the higher flows to bypass the system and continue to flow in the storm main.
The pretreatment swirl concentrator is a Vortechs 16000 unit from Contech, capable of treating 30 cubic feet per second of runoff. It separates out large debris and trash. The City of Seattle and SPU designed this part of the project.
Fuesel says the project takes drainage from 435 acres and will handle “all of the flow up to a little over 7.2 cubic feet per second, or 3,200 gallons per minute, when everything is complete. It doesn’t correlate directly to a certain storm. There is a provision for increasing the flow to roughly 9.4 cfs (4,200 gpm). These are flowing full rates.”
When all four swales are installed, they will treat 190 million gallons of stormwater annually. Fuesel hopes that the Swale on Yale will inspire similar projects.
“Coordinating takes a lot of time. We coordinated with everyone involved—the developer, the City Design Commission, SPU, KPPG, everyone. This project was 10 years in the making,” he says.
Credit: City of Bellevue
Installation of water-quality vault in Downtown Park
Point Defiance Regional Stormwater Treatment Facility
As cities and communities of western Washington consider stormwater planning and projects in light of how they can contribute to the overall health of Puget Sound, regional stormwater projects increase in importance. One such example is in the city of Tacoma.
The Point Defiance Regional Stormwater Treatment Facility is located at the entrance of Point Defiance Park, a city park. It was completed in December 2015 after five months of construction. This regional facility is a joint project of the City of Tacoma and Metro Parks Tacoma.
“The City’s partnership with the parks department was key to success of this project,” says Jessica Knickerbocker, City of Tacoma engineer and project manager, adding that parks department officials supported the extra effort and time needed to create an outstanding project.
The 5,500-square-foot project takes an innovative approach to managing stormwater. It does so with such visual clarity that even a casual park visitor can see how the facility works—no need to read interpretive signage.
“It’s a facility that can speak for itself,” declares Knickerbocker.
The purpose of the project is to capture the worst pollutants before they reach Puget Sound. The sound is already polluted with heavy metals from the Tacoma Smelter Plume, an area where smelting operations took place for years.
Stormwater drains into the facility from a 750-acre watershed that lies entirely within the Tacoma Smelter Plume. The facility can treat 8 million gallons of stormwater daily.
“One of the biggest challenges was that the project was designed entirely from scratch. There were no models to learn from. Every element of it had to be engineered,” says Knickerbocker. “Lots of hydraulics went into [the project].”
So did lots of trial and error and “adjustability. We couldn’t treat all of the stormwater. We had to split the flow to treat smaller [storm] events. We had two flow splitters,” explains Knickerbocker.
And then there were the models. “We had our models based on three years of meter data. Parametrix had their own model flow and Contech had their model flow. Still, there was so much flow getting into the 54-inch-diameter pipe that we had to add in a slide gate.”
A StormGate high-flow bypass structure from Contech closed a 24-inch-diameter pipe down to allow only 6 inches of open space for runoff flow. Now the system’s six large pools “generally can handle short outbursts up to 12.4 cubic feet per second.”
Before choosing what would be the more difficult—but more effective—stormwater treatment approach, City of Tacoma officials considered various options. One was to retrofit every street corner with its own bioretention system. However, the estimated cost of $15 million compared to the innovative facility’s cost soon eliminated this possibility.
The total cost of the regional treatment facility was $2.4 million. The City of Tacoma’s Surface Water Department funded $1.4 million of the cost, and the Washington State Department of Ecology contributed $1 million. “The project wouldn’t have been possible without the grant from the state Department of Ecology,” says Knickerbocker.
Credit: City of Tacoma
Tacoma’s Point Defi ance Regional Stormwater Treatment Facility
The Point Defiance stormwater facility works by gravity. It is located at the park’s entrance, which is the highest point of land. Stormwater flows to a CDS hydrodynamic separator for pretreatment before it enters the bioretention facility. The CDS uses swirl concentration and continuous deflective separation to remove trash, sediment, and other debris from the runoff. This arrangement also saves time and labor costs by providing one single point for maintenance.
The bioretention section contains a series of cascade pools, distribution channels (troughs), and nine precast Filterra Bioscape treatment cells from Contech Engineered Solutions. The Filterra cells contain an engineered media, a blend of washed aggregate and organic material, created to operate at high flow rates (100 inches per hour). As runoff moves through the cells, pollutants are removed by the media.
The treatment cells are 10 feet wide and range in length from 30 to 100 feet. The cells are topped with mulch and evergreen huckleberry and other native plants.
The treated runoff moves from the underdrain system to a bioswale. From there it is sent to the Point Defiance Marina and Commencement Bay.
Knickerbocker says that the stormwater facility “does seem to be performing as we anticipated. We’re monitoring how much sediment is collected on the mulch, figuring out the optimum time [interval] for maintenance.”
Parametrix served as design engineer for the project. Landscape architecture was by Site Workshop. The general contractor was Ceccanti Inc. Precast concrete components were provided by Oldcastle Precast.
The project was awarded the 2016 Green Infrastructure Award from the National Association of Flood and Stormwater Management Agencies. It won a Silver Award for Engineering Excellence at the American Council of Engineering Companies 2017 awards.
Port of Olympia
The Port of Olympia, WA, is the southernmost deep-water port on Puget Sound. Its Marine Terminal handles a great volume of cargo bound for ports around the world.
That cargo includes timber—lots of timber—because it is one of Washington’s major industries. More than 130 million board feet of logs move through the Port of Olympia’s Marine Terminal each year.
“We have a sense of pride that we’re celebrating Washington’s heritage as a timber state. And for every tree harvested, three are planted, so it’s a renewable resource we’re handling,” says Rachel Jamison, director of environmental programs for the Port of Olympia.
The logs leave behind bark and other bits of organic material that wash into south Puget Sound. Bacteria act on this organic matter, causing it to decay. The process depletes the oxygen in the water, which contributes to the decline of aquatic life.
The state’s industrial stormwater permit includes rigorous benchmarks for stormwater containing oxygen-depleting material. Along with other log yards in the state, the Marine Terminal at the Port of Olympia has to treat its log yard runoff to meet these benchmarks.
The chemical oxygen demand is the most difficult benchmark to meet.
The average annual rainfall in Olympia is 52 inches. That number translates into 64 million gallons of stormwater that the Marine Terminal must treat each year.
Jamison says the Marine Terminal stormwater team considered bioremediation, but determined that it wouldn’t be enough to reach the benchmarks. Instead, the solution chosen that would allow the Marine Terminal to meet the requirements is contained in a separate facility. It covers 3.25 of the Marine Terminal’s 65 acres. “We’re the first port in the state to use wastewater technology to treat our stormwater,” says Jamison.
She adds, “We take our location and proximity to Puget Sound seriously. Hence, we made a $12 million investment in our stormwater treatment system.”
The stormwater treatment facility includes a three-cell system for oxidation, pH adjustment, and settling and a group of back-flushing sand filters. A pond and handling facilities deal with collected sludge. A treatment building is the final component. A decant pad holds debris from street sweeping and catch basin cleaning.
The system has flexibility to meet future needs. Its various parts are modular so that it can easily be increased or reduced in size. An existing stormwater pond was retained as a possibility for future polishing and or backup capacity.
The Marine Terminal’s treatment facility began operating in October 2014. In late January 2015, employees discovered that the hydrogen peroxide system (part of the stormwater treatment facility that reduces chemical oxygen demand levels before discharge) had failed. Hydrogen peroxide leaked into the sanitary sewer system and a very small amount went into the storm system. No hydrogen peroxide reached Budd Inlet, the closest body of water. In a few days the stormwater facility, except for its hydrogen peroxide system, was back in operation.
Testing revealed a design flaw, which was eventually corrected, and the new version was then approved by the Washington Department of Ecology. The facility went back to full operation earlier this year.
Not enough time has elapsed to tell exactly how well the new system is working. Jamison explains, “We’re in the process of doing final calculations now.”
She says the Marine Terminal’s innovative stormwater system “could be used in a similar port setting at the nexus between stormwater and a major waterway.” She notes that the biggest challenge for the Marine Terminal’s stormwater facility—besides the hydrogen peroxide incident—is “ensuring that the staff has the resources they have to have to manage day-to-day operations.”
This innovative stormwater treatment facility has won numerous awards, including the American Public Works Association’s 2015 Project of the Year and the Green Business of the Year Award from the Olympia Chamber of Commerce.