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Evaluating Stormwater and Sweeping on the World's Longest Floating Bridge

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Paul Fendt, PE, is a water resources consultant who works for Parametrix, a 100% employee-owned ESOP organization that in 2019 was voted one of Washington State's Top 100 companies to work for. Paul has 36 years of experience in his profession and was chosen as a central figure in the three-year BMP development and monitoring effort on the world's largest floating bridge.

In the accompanying Zoom interview, Fendt discusses the project with WorldSweeper's editor, Ranger Kidwell-Ross.

by Ranger Kidwell-Ross

What is known specifically as the Seattle SR 520 floating bridge is a replacement bridge for the previous crossing structure. Over 7,000 feet of it floats on the body of water it crosses, Lake Washington, which is nearly 22 miles long with an area of approximately 34 square miles. As one might imagine, keeping the lake as pristine as possible is a very desirable outcome and conveyance of stormwater to the ends of the bridge is infeasable for a variety of reasons.

So, first considered were All Known, Available, and Reasonable methods of prevention, control, and Treatment (AKART). These included four technology categories:

  1. Media filtration vaults with conventional sweeping
  2. Catch basin filtration with conventional sweeping
  3. Modified catch basins/cleaning with conventional sweeping
  4. High-efficiency sweeping and modified catch basin/cleaning
The 'treatment train' that won out was the combination of:
  1. High-efficiency street sweeping
  2. Modified catch basins
  3. Spill containment lagoons
The sweeping portion of this effort includes sweeping once per month during the first four days of the month. The sweeper cleans over 8,000 feet of bridge at between 6 and 9 mph. Due to the safety considerations, the operations train includes the following five vehicles:
  1. Advanced warning vehicle
  2. Truck for collecting large debris
  3. Broom sweeper
  4. Regenerative air or vacuum sweeper
  5. Truck mounted attenuator

Although the main target of pollutant abatement was copper, as you will hear there are other pollutants considered, as well. If you would like to know more, we encourage you to watch the Zoom presentation linked below, which is hosted at YouTube.

ParametrixLogo250 Paul Fendt and Parametrix have also made the Powerpoint presentation used in the Zoom interview available for download at this link. If you would like to contact Paul, you may reach him via email sent to

In the event you are unable to view the YouTube file embedded below, or would like to forward the actual YouTube link for the video to others, the address of the video is: (opens in a new browser window)

In the event you have questions or comments for Kidwell-Ross, you may reach him at this email address.

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