How Much Petroleum Enters Puget Sound In Stormwater?

Clearing up the confusion about stormwater pollution.
This post is part of the research project: Stormwater Solutions: Curbing Toxic Runoff

How much petroleum is there in the stormwater pollution that enters Puget Sound? That question has lately generated a good deal of confusion and obfuscation. So let’s take a moment to get the facts straight.

You can think of stormwater pollution as a set of Russian dolls. The biggest doll is total toxic pollution. Inside that doll, and nearly as big, is oil & grease. And inside that doll is petroleum hydrocarbons. Here’s how they stack up, size-wise:

Low-end estimate (annual average):

  • Total toxic pollution: 14 million pounds
  • Oil & grease pollution: 13 million pounds
  • Petroleum pollution: 7.9 million pounds
  • Petroleum is 58 percent of all toxic stormwater pollution.

High-end estimate (annual average):

  • Total toxic pollution: 94 million pounds
  • Oil & grease pollution: 92 million pounds
  • Petroleum pollution: 55 million pounds
  • Petroleum is 58 percent of all toxic stormwater pollution.

You might think that there are pretty big differences between the high and low ends of the ranges, and there are. But let’s be clear about where the uncertainty lies: it’s about the total volume of stormwater pollution entering Puget Sound. What’s not uncertain—what we actually do know with some degree of precision—is that virtually all of the pollution is oil & grease and that the lion’s share of oil & grease is petroleum.

In other words, petroleum represents more than half of all toxic pollution entering the Sound in stormwater.(It’s likely about 58 percent, to be precise). By volume, petroleum is the single largest pollutant entering the Sound.


Notes and sources: The numbers I’ve presented here for total toxics and oil & grease are the latest—the new January 8, 2010 numbers—released by Washington’s Department of Ecology as a recalculation of their “Phase 2 Study”. The figures for petroleum pollution are conservative calculations based on the best available scientific understanding of the problem. They assume that 60 percent of oil & grease is petroleum, a rough-and-ready assumption that is based on scientific studies in Washington and other places in North America. (Previous estimates in the Phase 2 study put the numbers for petroleum pollution at much higher levels.) “Low-end estimates” refer to a 75 percent probability of exceedance, which is basically a fancy way of saying 25th percentile. High-end estimates refer to a 25 percent probability of exceedance, or the 75th percentile. Mostly likely, the actual numbers fall somewhere between the two estimates.

To write this post I consulted with the lead researchers at the Department of Ecology. You can find more information at the Department of Ecology’s summary sheet, Focus on Toxic Chemicals in Puget Sound. Also, Table 5 of the technical memorandum Addendum 2: Phase 1 and Phase 2 Toxics Loadings Reports (where figures are given in million metric tons rather than pounds). Of further interest is Addendum 1: Comparison of Loading Estimates to Puget Sound for Oil and Petroleum Products.

Update 1/19/10: Lisa Stiffler dug into the technical documentation and offered some minor modifications to the original numbers that I posted. (New numbers in the tables above may not appear consistent due to rounding.)

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  1. Stefan says:

    What is the time frame for these figures? Per annum? Total historical? Since when? Anyways, it’s shocking.

  2. Matt the Engineer says:

    Do we know where this petroleum comes from? Is it from simple oil leaks in cars? Airborne products of combustion being washed down in the rain? Industry? Tires? Tar from the road itself? I suppose it wouldn’t be from fuel oil leaks, since most of us are on natural gas these days.

  3. Eric de Place says:

    Stefan-Good catch. They are average annual figures. I’ve updated the post accordingly.Matt-It’s a wide variety of sources: all of those you mention (though I’m not sure about tires) plus others, including fuel spillage. Also, I do think it’s reasonable to assume that there are leaks from aging fuel tanks that are present in surprising numbers in older neighborhoods. The lesson, I think, is that it’s a very difficult problem to address at the “source” because there are gajillions of small, disparate sources for petroleum pollution. Unless we have a way to capture it or treat it—through conventional stormwater infrastructure or low-impact development techniques—a frightening amount will end up in our waterways.

  4. angie says:

    why dont we outfit storm drains with filters?

  5. Tim Colman says:

    I hope someone mentions the hidden costs all this petro creates that gets shifted onto working people’s backs. Yet the companies that produce oil still get to call in quarterly profits.That is a game I have seen at a Mariner game where the screen lights up and you have to keep track of where the ball is under ever moving hats. My point is that there is a specious argument in the non point pollution in stormwater narrative. It is as if greens have colluded with giant corporations agreeing not to talk openly about the elephant in the room– greedy profit centered companies. Companies with quarterly profits to worry about don’t care about what happens once you use their product. That is true –unless you force them to by shaming or legislating. That is why this tax in Washington state on petro is important. It points a finger at a prime source of a lot of problems in our community and says you use it, you pay. Hopefully the tax will get high enough to actually shift energy purchases to greener, less costly “down the drain” costs later.To Angie’s question about why don’t we outfit storm drains, I want to know where the public works project jobs are that are not putting filters over storm drains, but ripping up all this impermeable pavement and paving with permeable concrete?We need the jobs and we need the water to perk through the ground. Recent story in the Seattle Times tells the story of homes sinking into the ground for peat’s sake! Why? Because the peat bog they are built on is drying up because of all the impervious pavement shunting rainwater down sewer and storm drains.We really need a clear picture of rewilding Seattle– the combination of pervious pavers and more swales, hedgerows and urban forests to mimic the ecosystem we cut down and paved over.Green roofs, green walls, solar panels, pervious pavers, hedgerows and swales on every sidewalk, biodiversity improvements, and finally stormwater that soaks into the ground and cleans itself the way God and Nature meant it to…

  6. Rick says:

    Stomrwater is a giant issue in Eastern Washington too. The City of Pullman is struggling to comply (and is not) with its stormwater permit impacting the Palouse River. PCBs and other stormwater pollutants flow into the Spokane River when it rains.

  7. Rick says:

    The Spokane Riverkeeper recently filed a notice of intent to sue the City of Spokane because the City’s stormwater system in the largest source of PCBs into the Spokane River. As a result, we have fish that we can’t eat and we pass the problem on downstream to the Spokane Tribe.See for more details.

  8. 8string says:

    It would be good to put this volume into context. I’ve heard that these amounts are analogous to the Prince Williams Oil Spill, but can we have some comparisons? If we are looking at low end estimates over 15 million pounds, what’s that comparable to? And on the high end? It’s all very hard to understand the magnitude of the problem, other than “it’s big”

  9. Frank Halstead says:

    I agonize over the indifference of both the public and the so called “green sensitive” Muni’s that refuse to evaluate existing technology that can economically yet very effectively largely reduce the amount of damage to our waterways caused in largely by used oil and other petroleum products leaked upon our streets and roadways by motor vehicles and other machinery and transported via stormwater drains to our waterways. Estimated to be as much as 60% of the water pollution problem, the answer lies in not allowing the contaminated substances to reach the roadways.That technology is now and has been available for several years but our Muni’s are indifferent (not convinced of petroleum damage via storm drains to waterways vs.possible costs} and the public is unaware of it’s exisistence and availability. More information available.

  10. Matt the Engineer says:

    [8string] I find per-person is usually a good way to get my head around large numbers. Let’s see: (14 to 94 million pounds per year of toxics) divided by (3.5 million people in the Puget Sound) = each of us dumps between 4 and 27 pounds of toxics into the sound every year.

  11. Peter Evans says:

    Considering we have DOE approval for oil treatment, why don’t more people consider using our innovatibe green product to retro fit stormwater catch basins or roadways? To learn more…go to and ask for a Design Assistance Kit to see how easy it is to size and specify Filterra to treat stormwater

  12. Donna Albert says:

    Does anyone know how much of this problem would be resolved if we no longer burned fossil fuels? I understand it is possible to transition to wind, wave, tidal and solar energy for all our energy needs, and battery-powered vehicles (Scientific American, November 2009 issue). Assuming that is the case, would that also solve this problem?

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