Echo Lake Stormwater Study

By Carly Greyell

Living in King County, rain is a natural part of life. But you might not realize that when rain collects on impervious surfaces, like roadways and roofs, it can pick up a variety of pollutants. Every day activities, like driving a car, walking the dog, and fertilizing your lawn, can contribute pollutants like heavy metals, oil, bacteria, solids, and nutrients. This polluted rain water is referred to as stormwater and King County and other local jurisdictions are working hard to reduce the amount of pollutants that stormwater adds to our local waterbodies, including lakes, rivers, and Puget Sound.

One way to treat stormwater is through bioretention where stormwater is filtered through a soil mixture that includes compost and sand. In 2012, the City of Shoreline installed a number of bioretention planter boxes (designed like concrete-lined rain gardens), along Aurora Avenue North, which is part of Highway 99. The bioretention planter boxes treat some of the stormwater that drains to Echo Lake. King County recently designed a study to see how effective the planter boxes remained three years after construction, and whether they could reduce stormwater pollutants that contribute to human health risks such as PCBs.


The King County Environment Lab (KCEL) Field Sciences Unit braved the rain to collect samples during eight storms from December 2015 to February 2017. Samples of both the untreated stormwater entering the bioretention planter boxes and the treated stormwater after it had filtered through the soil mixture were collected for chemical analysis. Pollutant concentrations between the treated and untreated stormwater were then compared to determine how effective the planter boxes were at removing pollutants from the stormwater.

The results were mostly positive: the bioretention planter boxes significantly reduced concentrations of most pollutants, including chemicals associated with oils and exhaust, total copper, total zinc, solids, and even PCBs. Average reductions for these pollutants ranged from 81 percent to 99 percent at each site. Levels of dissolved heavy metals were not always reduced, but concentrations in both the treated and untreated stormwater were very low. These findings are consistent with results from studies that evaluated new bioretention, suggesting the planter boxes are continuing to perform as expected, three to five years after installation.

Unfortunately, nutrients in the stormwater were not consistently reduced, and in many cases the stormwater treated by the planter boxes actually had higher concentrations than the untreated stormwater. This is particularly problematic for phosphorus, which, when elevated, can lead to increased algal blooms in lakes. This problem has been recognized with bioretention across the region, and local researchers are currently evaluating alternative bioretention soil mixtures for stormwater treatment in areas at risk for algal blooms.


Despite the good news in treatment, the maintenance requirements for these planter boxes were higher than expected. Water enters these installations from the busy roadway through cuts in the curb, which were easily blocked with dirt, leaves, and other debris. Without regular debris clearing, stormwater was blocked from entering the planter boxes, and bypassed treatment.

Thanks to the results of this and similar studies, stormwater engineers and managers are learning how to improve stormwater treatment techniques.

PCBs – Banned But Not Forgotten

pcbsPolychlorinated biphenyls, or PCBs, are a group of chemicals developed in the 1930s that had a range of uses, including additives for construction materials, such as paints and caulks. However, PCBs were linked with negative health effects such as cancer and hormone disruption, and in 1979, U.S. production was banned. Unfortunately, most PCBs do not break down easily, and older buildings and industrial sites remain important sources of PCBs.

In several local waterbodies, including Lake Washington, fish consumption advisories warn that certain fish species contain PCBs at levels that are unsafe to eat. Researchers are learning that one of the main ways PCBs enter these water bodies is through stormwater. However, PCBs are not currently regulated under stormwater permits. Studies, like the one described here, are important so that we can learn how best to reduce PCBs in stormwater, thus preventing human health issues.

Effective Stormwater Management

The Washington State Department of Ecology helps local municipalities like King County and the City of Shoreline manage their stormwater permits. Since 2013, most Washington state stormwater permitees have pooled resources to fund regional stormwater monitoring and studies that evaluate how well permit requirements serve to improve stormwater treatment. Washington state permitees selected the study described here for funding through this program.

carly-greyell.pngCarly Greyell is an ecotoxicologist in the King County Science and Technical Support Section. She has been supporting many of the Lower Duwamish source control projects and involved in ongoing toxics monitoring and projects assessing the effectiveness of stormwater treatment.




Modeling Climate Change Impacts on Extreme Precipitation, Stormwater Design Requirements, and Wastewater Conveyance

By Jim Simmonds

King County’s 2015 Strategic Climate Action Plan calls for assessments of climate change effects on large rainstorms in King County and the ensuing impacts on stormwater and wastewater management. These assessments were prioritized in response to recent findings from the University of Washington that large rain events known as “atmospheric rivers” are projected to hold an average of 22 percent more moisture by the end of the century (Warner et al., 2015).


Large rain events known as “atmospheric rivers” are projected to hold an average of 22 percent more moisture by the end of the century.

(Warner et al., 2015)

Most extreme precipitation events along the West Coast are associated with winter atmospheric river events. Atmospheric rivers are relatively long, narrow bands of moisture-laden air that can deliver intense rain when they intersect land. Atmospheric rivers that affect western Washington often originate in the subtropical Pacific Ocean near Hawaii; these are sometimes referred to as “pineapple express” events. About one-half to two-thirds of Western Washington’s annual precipitation falls during atmospheric river events.


King County partnered in 2016 with the University of Washington’s Climate Impacts Group to model hourly rainfall throughout the county under climate change conditions. This modeling was funded by King County’s Stormwater Services Section,Wastewater Treatment Division, and a grant from the Washington State Department of Ecology. The innovative modeling approach relies on “nesting” a regional weather model within two global weather models to allow for more refined predictions. The nested modeling approach is critical for understanding climate change impacts on storms in the Pacific Northwest.

This image of total precipitable water contained in the atmosphere shows a long band of wet air crossing the Pacific Ocean towards the Pacific Northwest, known as an “atmospheric river” (from Warner et al 2015).

The regional model used was the Weather Research and Forecasting model applied by the University of Washington, which is the same model used to make short-term weather forecasts for the region. The climate scenario modeled is based on ongoing, unabated global carbon emissions through the end of the century.

Preliminary modeling results show about 20 to 40 percent more rain will fall during each year’s heaviest hour of rainfall by the end of this century. Increases are also projected for less-frequent storms and longer-duration storms. For the official Seattle weather station at SeaTac, this means that the one-hour annual peak rain event is projected to increase by 2100. Model results to date do not suggest that “atmospheric rivers” will occur more frequently under climate change conditions, only that they are projected to deliver more precipitation.

These modeling results have important implications for stormwater management. In accordance with requirements by the Washington State Department of Ecology, King County requires developers to use a manual to size and design stormwater flow control and water quality treatment. The design relies on the past 68 years of rainfall data for ensuring proper sizing. Because future storm sizes are projected to increase, this implies that stormwater systems designed today may be undersized for future conditions. A sensitivity analysis of stormwater facility design to future rainfall conditions will be completed in 2018, along with an analysis of options for updating the design requirements.

Intense rainstorms can overwhelm the stormwater system and cause urban flooding.

King County also owns and operates the regional wastewater conveyance and treatment system for the greater Seattle area. Portions of the City of Seattle have combined wastewater and stormwater conveyance systems, which allow for substantially greater flows during rain events than dry periods. King County is investing heavily to reduce overflows from the combined system during large rain events, and is interested in incorporating future storm conditions in the planning process. To do this, the King County Wastewater Treatment Division will be modeling the wastewater conveyance and treatment system under both historical and projected future climate conditions to determine possible changes in flow timing and volume. The results from this modeling will be incorporated into future plans for maintaining and upgrading the facilities.


Read more about the King County SciFYI newsletter.

jim-simmondsJim Simmonds is the Water Quality Unit Supervisor of King County’s Science and Technical Support Section. He has over 25 years’ experience monitoring and modeling environmental conditions, managing environmental investigations, managing environmental data, and assessing potential impacts of stormwater, wastewater, and environmental contamination. He has been with King County for 17 years.


Semhar’s story (or, how to turn water in to work)


Abraha Semhar

Growing up in Eritrea, Semhar Abraha and her family relied on monthly tankers to fill her community’s water reservoirs.

“Everyone in our community would light up when they heard the tankers blow their horns,” said Ms. Abraha.

There was no tap water in her home and water was limited. Her family used the water from washing dishes to flush the toilets. None of it went to waste.

“I watched my mother manage our drinking water and the water for our small vegetable garden,” said Ms. Abraha. “My father is an economist and always has a way of making things more efficient.”

Ms. Abraha attributes her desire to have a career in water management to her parents.

Ms. Abraha chose to pursue an education in engineering in Eritrea where she worked on government water projects such as designing water harvesting and irrigation structures, diversion structures and water canals.

In her research she learned that Eritrea, bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast of the Horn of Africa, is not actually a water scarce country. But the lack of technology available made water scarce to those who live there.

“Eighty percent of the population are farmers but they aren’t using water efficiently,” said Ms. Abraha.

In Eritrea, Ms. Abraha was working as a junior engineer to help build one of the country’s biggest dams when she decided to pursue a Master’s degree in Civil Engineering and came to Seattle to attend the University of Washington.

After completing her degree, Ms. Abraha became the first trainee in the new Stormwater Services Engineering Internship Program. This pilot program is part of the King County Water and Land Resources Division’s equity and social justice work that is designed to train future engineers from under-represented populations in the field of engineering.

“People here are so collaborative. Everyone is willing to help you and teach you things,” said Ms. Abraha.

During her internships Ms. Abraha trained on survey, CAD and asset management projects and has accepted a 3-year position as an Engineer I in the Wastewater Treatment Division.

Ms. Abraha believes that there may come a time when she returns to Eritrea, perhaps to help build a wastewater treatment plant there, but right now she is busy here realizing her dream.