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9601 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7608
Fax: 206.275.7814
Email: publicworks@mercer. . .
Hours: 7:30 AM - 4:00 PM (Mon-Fri)
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City of Mercer Island / Public Works / Stormwater Utility

Stormwater Utility

Stormdrain manhole
Stormdrain manhole

The City’s Stormwater Utility is responsible for managing, maintaining and improving the drainage systems on Mercer Island. Our goals are to improve the quality of water that runs off into Lake Washington, and to reduce erosion and flooding problems on the Island.
There are more than 3,000 catch basins and 285,000 feet of storm drain lines on Mercer Island. We inspect storm drain lines every year; they are cleaned as needed and continually assessed for erosion control measures, according to City, State and Federal rules and regulations. The City relies on contracted services for open ditch and catch basin cleaning.
The City of Mercer Island must meet specific requirements to implement programs which minimize the discharge of pollution from municipal stormwater systems into our streams, lakes, rivers and wetlands. The 2019 Stormwater Management Program (SWMP) Plan details actions the City is taking to reduce stormwater runoff pollution to Lake Washington.

What's New?  

Mercer Island Benefits from Bioswales
A bioswale is a gently sloped drainage path filled with vegetation; its design helps remove silt and pollutants from runoff water before it enters the stormwater system or another body of water. Bioswales are often installed to protect ecologically sensitive areas or added around parking lots to reduce the amount of automotive pollution released directly to the storm sewer. In this article from the Mercer Island Reporter, learn how Crest students worked with the City of Mercer Island’s Stormwater Utility to install a bioswale that will protect the Ellis Pond neighborhood for years to come.
Trees Protect Mercer Island from Stormwater Runoff
For years the City has made preserving and adding trees in parks, open spaces and the public right of way a high priority, and now the focus is starting to turn to the rest of the Island.
During the 2009-2010 Biennial Budget process, the City Council authorized a new effort aimed at growing the tree canopy on private property. For the first year, the goal set by Right of Way Arborist, who coordinated the effort, was to get residents to agree to plant 200 trees at their homes.
The trees were made available at a substantially reduced price of $5 each and were distributed in fall 2009 at the Farmers Market and in conjunction with the City’s Recycling Event in October. Two native species, vine maple and excelsa cedar (a smaller cousin of the western red cedar), were offered. The goal was easily achieved, with 285 trees finding new homes.
The cost of the program for the year was just under $5,000. The sustainability benefits of that investment to the Island’s environment over time will be tracked through urban forestry modeling software. The most readily measured benefits will be the trees’ ability to capture and store carbon dioxide and to offset the impacts of stormwater runoff.
Each year the “value” of the first 285 trees will grow, and as more trees get planted, the contribution that Island homes are making to a sustainable Island will become substantial. To put this in context, one study in California found that 100 trees over the course of 40 years can capture as much as 600,000 pounds of carbon dioxide and hold back as many as 1.6 gallons of stormwater runoff. 
Puget Sound Starts Here
The City of Mercer Island is taking part in a campaign to build awareness throughout the region about stormwater. Mercer island was one of many jurisdictions that cooperated with King County and the Puget Sound Partnership to develop the 'Puget Sound Starts Here' campaign.
We will be looking for ongoing ways to reach out to residents, to help you understand how you can have a positive impact on the health of our waterways (and ultimately Puget Sound) by scooping pet waste, taking cars to a commercial car wash and having oil leaks fixed, and using fertilizers and pesticides sparingly.
The new campaign includes TV commercials and other communication channels. Public education about stormwater is an essential part of the City's National Pollutant Discharge Elimination System (NPDES) permit compliance.

What is Stormwater? 

Stormwater is rainfall which is not absorbed into the ground. Instead, it runs off roofs and down streets and sidewalks, into storm drains and eventually into Lake Washington. Stormwater is not sent through our public sanitary sewer system for treatment. Therefore, when it rains, contaminants on roads and other surfaces are washed into the nearest storm drain and eventually into Lake Washington.
Stormwater pollution results from everyday things such as automotive leaks, pesticides and fertilizers on your landscape, washing your car, pet waste and other activities that allow small amounts of contaminants into our storm drains. To improve stormwater quality, we must reduce contaminants and prevent them from entering Lake Washington.
Therefore, we are working to improve the public’s understanding of the importance of protecting stormwater quality, to prevent spills and illegal dumping and improve home and landscape practices. There are a number of things you can do to reduce stormwater runoff pollution.

Reporting a Spill? 

Help us keep Lake Washington clean. If you see a spill or illegal discharge into a city stormwater drain, report it right away.  Call (206) 275-7608 (daytime) or (425) 577-5656, our after hours 24/7 dispatch number.

Stormwater Permits 

The City provides helpful information regarding stormwater permits, when they are required for private development projects, and the types of drainage improvements required. There are links to stormwater design manuals, guidance documents and maps. Information regarding low impact development is also available.

Stormwater Pollution Prevention Plans (SWPPPs) 

The City of Mercer Island is covered by the Western Washington Phase II Municipal Stormwater Permit, issued by the Washington State Department of Ecology (Ecology) in 2007. This permit is issued as part of the National Pollutant Discharge Elimination System (NPDES) Phase II program, which, in the state of Washington, is regulated by Ecology. As a Phase II community, Mercer Island must prepare Stormwater Pollution Prevention Plans (SWPPPs) for all heavy equipment maintenance (including fueling activities) or storage yards, and material storage facilities owned or operated by the City. Therefore, the City of Mercer Island has SWPPPs for:

Stormwater Management Program (SWMP) Plan 

The National Pollutant Discharge Elimination System (NPDES) Phase II Municipal Stormwater Permit was issued on January 17, 2007, by the Washington State Department of Ecology under the provisions of the U.S. Environmental Protection Agency's Clean Water Act. In Western Washington, 80 cities and five counties must comply with the permit.
The permit has specific requirements and deadlines for implementation of programs to minimize the discharge of pollution from municipal stormwater systems into our streams, lakes, rivers and wetlands to protect their beneficial uses (such as swimming, boating, fishing and aesthetics) and other environmental resources. The City of Mercer Island is classified as a ‘small’ municipal separate stormwater sewer system ("MS4" - click here for latest annual report).

Each year's Plan (SWMP) details actions the City is already taking to reduce stormwater runoff pollution to Lake Washington, and expands on those actions as needed to comply with the new permit requirements. 
Recent City of Mercer Island Plans:


You can help!
There are things you can do today to help reduce stormwater runoff pollution. For a list of helpful tips, click here.

If you see illicit discharges, dumping or spills, please contact the Public Works Department at (206) 275-7608 during regular business hours. Outside of business hours, please call (425) 577-5656, our 24/7 dispatch number.

The City is also seeking comments from citizens about the City's Stormwater Management Program. If you have any comments you would like to share, please Email Public Works.

For more information:
Current Stormwater Management Program (WSDOE Stormwater Mgmt Manual for the Puget Sound Basin)
WSDOE Western Washington Phase II Municipal Stormwater Permit Website


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