A (seemingly) long time ago, in a neighborhood not so far away at all…it was raining, and raining pretty hard. I was out walking, and turned south down Thackeray. There was a steady stream of rainwater flowing downhill. As is often the case here in the city, especially when it’s been a while since the last rainfall, there was a very noticeable oily sheen in the water as it cascaded down along the curb. I don’t THINK this was attributable to the oil change business there on NE 45th, it might have been from one or more of the customers who stopped there. But oil sheens on wet streets and parking lots are far from uncommon. The next time we get a decent rainfall, check out the parking lot at QFC or at the Ballard Fred Meyer. Look at the water in any marina anywhere in the country. Oil sheens are everywhere.
In my previous life, I thought a lot about oil sheens and more, as I responded to oil and chemical spills around the country. Before that, I worked on monitoring coastal pollution. So, here’s some perspective from where I sit in the cheap seats (I should mention that I contacted Seattle Public Utilities for help and input on this article…but never heard back, ahem). There’s not a lot of oil in an oil sheen, as it is molecules-thick on the surface of water. Most of the time, there’s so little oil in rainbow sheens that the designated responders like the Coast Guard, EPA, and Washington Ecology don’t do anything to recover it—there’s very little return on the effort to try and soak it up, and that’s usually done with sorbent materials that have to be disposed of someplace. That’s typically a landfill. You wind up putting a fair amount of plastic in that landfill to recover micro-liters of oil.
Like many environmental problems, there’s a flip side to the coin. Yes, there’s only a tiny amount of oil in oil sheen. But with all the cars and all the streets and all the rain in Seattle, the tiny amounts of oil can—and do—add up. While the volume of oil you see on the rainwater runoff is miniscule, if you multiply that by the total amount of rainwater flowing on all the streets in the city…it’s a lot of oil. In 2022, the National Academies of Science, Engineering, and Medicine estimated 1.2 million tons of oil entered North American waters from surface runoff, by far the largest source among many. This is called nonpoint source pollution. That is, rather than a point source, like a factory outfall, it’s a many-sourced low volume input that is considerable simply because there’s so much of it. And all of this low concentration but high volume input is going…somewhere. But where?
That brings us to the fairly massive and seemingly interminable construction project that’s been going on at the southern end of Stone Way. Day-to-day, most of us think of that project as a big pain in the…commute. And yes, it HAS dragged on FOREVER. But let’s zoom out, and connect it to my rambling story here.
This construction project—officially, the Ship Canal Water Quality Project—is part of a large-scale effort by Seattle Public Utilities to improve the handling of stormwater runoff containing oil and many other pollutants that urban life generates. Most of the time, runoff from the streets is collected and diverted to water treatment plants (like the primary one in Discovery Park) where the worst of the contaminants and all of the other stuff we carelessly discard into the environment are captured and treated—along with our sewage. But during heavy rainfall events, the in-line piping and storage is overwhelmed. The untreated excess gets released directly into surrounding waters: Lake Washington, Lake Union, Puget Sound. That’s why, after heavy rains, beaches around the region sometimes are closed because of high bacterial counts: raw sewage and untreated stormwater overflows into the lakes, rivers, and the Sound.
That project at the end of Stone Way is a major effort to address some of this problem, by providing a tunnel to divert stormwater toward Ballard and a holding facility, where the untreated stormwater and sewage can be retained, controlled, and eventually directed into the treatment plant.
Returning to the colorful oil-tainted stream that flowed down Thackeray toward the lake…in the old days, it would have continued its gravity-driven journey straight into Lake Union. When the city built its stormwater and street drains, the ability to divert runoff to the city’s fairly sophisticated wastewater treatment plants was provided—but with a limited capacity. But the big tunnel project that’s been blocking Stone Way since woolly mammoths roamed Wallingford will greatly improve how stormwater is handled here and in adjacent neighborhoods, and most importantly—will help to reduce the contaminant loads affecting Lake Union and the Sound.
