• Alyssa Barton

What’s That Smell? CSO’s and Why We Still Have Them


I recently wrote about how cigarette butts are a pollutant - but do you know how our storm sewer systems work?

Cigarette butts can be washed down storm drains and out into local streams and rivers. This situation happens when you have what’s called an MS4 – a Municipal Separate Storm Sewer System. With MS4’s, you have sewer lines (pipes in a system that carries folks' wastewater from homes and businesses to a sewage treatment plant), separate from storm sewer lines (pipes in a system that carry rainwater, aka “stormwater,” from the storm drain to a stream, river, or other waterbody). The stormwater from MS4's flows out to waterbodies in what’s called a Sanitary Sewer Overflow, or SSO.

Sometimes, though, you have a system with combined sewer and storm sewer lines. This is called a Combined Sewer System. The benefit of a Combined Sewer System is that water from our storm sewer pipes - our stormwater, perhaps carrying things like cigarette butts - gets carried to the sewage treatment plant to be treated. This is great, since stormwater is the number 1 source of toxic pollution to Puget Sound. Though, not necessarily so great, since our sewage treatment plants don't all use sufficient technologies to treat toxic pollutants!

Rainwater flowing over developed surfaces can pick up oil, grease, and heavy metals from cars and tires, chemicals from man-made surfaces and structures, and litter and other pollutants off streets. Treating stormwater at our wastewater treatment plants is ideal because it helps remove debris and chemicals from the water before it dumps into our local waterbodies. However: the downside of Combined Sewer Systems is that they are limited in capacity. In Seattle and King County, in particular, sometimes it rains so much that the quantity of stormwater plus wastewater from our homes and businesses exceeds the system’s capacity. When this happens we get Combined Sewer Overflows - "CSOs" - a mix of raw sewage and stormwater that backs up through the pipes and into our local waterways.

Here’s a great illustrative photo from the interwebs - Washington’s Department of Ecology has an image just like this on file.


The above diagram shows how, when there’s a storm event and you have a combined sewer system, you can get a rush of too much stormwater flooding into the system and so the combined lines overflow. (See the upper righthand square). This situation results in a lovely, pungent, sludgey brew of raw sewage (10% or less) mixed with stormwater (90%+) polluting our waters. A CSO event.

This is similar to what happened when the West Point treatment facility at Discovery Park in Seattle experienced a bypass in February of 2017. https://www.seattletimes.com/seattle-news/environment/king-county-fined-361000-over-west-point-treatment-plant-failure/


Here’s a photo of the mix of stormwater and, err, poo water, from the bypass at West Point on February 16th, 2017. (Copyright: Seattle Times). Notice how, unlike in the diagram previously shared, the water is, in fact, visibly poopy.

West Point was an extreme example of a treatment plant unable to handle inputs of stormwater – though the failure resulted from several system malfunctions. However: CSOs happen all the time.

King County offers a real-time map that shows all the combined sewer outfalls around Seattle, and reports when a CSO event is happening near you. https://www.kingcounty.gov/services/environment/wastewater/cso-status.aspx

Why is this happening? How is it that cities and counties are allowed to knowingly operate waste treatment systems that sometimes don’t function, shooting millions of gallons of untreated sewage and stormwater into our waters? Doesn’t the Clean Water Act protect against this kind of thing? All good questions you might ask.

Well, as to the why: lots of cities around the nation are on Combined Sewer Systems – one EPA webpage says there are 772 municipalities on combined systems nationwide. There are a dozen or so municipalities around Puget Sound on Combined Sewer Systems, but Seattle and King County are by far the largest, and might be the only two that have not yet "controlled" their overflows. Perhaps city planners didn't take into account things like explosive population growth and climate change increasing wet weather events at the time these Combined Sewer Systems were engineered. The population of Seattle and the Puget Sound region is rapidly growing – per worldpopulationgrowth.com, Seattle has grown from just 1,150 people in 1870 to an estimated population of 659,000 in 2014. The Puget Sound Regional Council estimates that the region will grow to 1.7 million by 2040. And, per most sources, severe storm events are getting worse nationwide, while in Seattle, things are getting wetter. More people + more water = more CSOs. Combined Sewer Systems just weren’t designed to handle the excessive loads they sometimes now face.

As for the “how are we allowing this” question: well, starting in the 1990’s, the EPA tried to start doing something about CSOs nationwide under the Clean Water Act. The Agency started working with municipalities to reduce CSOs, and in Washington State, EPA sued King County and Seattle under the Clean Water Act for its excessive overflows. Rather than immediately stopping the pollution, in 2013 the parties entered into what’s called a consent decree, or settlement agreement. Both Seattle and King County agreed to reduce their CSOs to meet Washington State's CSO standard of 1 CSO event per year per outfall by December 31, 2030. By 2030! That’s a long ways a way, and that’s still one huge smelly nasty event per year that’s allowed per outfall - with no limit placed on the quantity, or types of pollutants that might be in the CSO. Seattle has jurisdiction over 87 CSO outfalls, King County has 39.

But that is all that EPA will require. And, that will get us a whole lot closer to no CSOs than where we’re currently at. One thing you should know regarding the Clean Water Act: it actually doesn’t prevent pollution. It allows it. I’ll get into this a lot more later, but in short, it’s a major flaw, and that’s why Washington State was allowed to set a standard of 1 CSO per outfall per year.

In order to prevent more CSOs from happening, municipalities can separate out their sewer and storm sewer lines (which isn’t ideal, because then stormwater won’t get treated at all), build extra treatment facilities, or build storage tanks to hold excessive stormwater during storm events until such time as it can be treated.


Another option is green stormwater infrastructure.


Image of green stormwater infrastructure in West Seattle,

courtesy of King County Wastewater Treatment Division’s website.

GSI is an approach to water management that protects, restores, or mimics the natural water cycle. Some types of green infrastructure include raingardens, rain barrels, streamside buffers, planting native trees and vegetation, and permeable pavement – these help slow the flow, store, and/or treat stormwater, and can help prevent CSOs by reducing stormwater inputs into Combined Sewer Systems.

If I didn’t mention it before, raw sewage often contains bacteria and pathogens that can make people sick, pollute our waters, and results in swimming beach and shellfish bed closures. It would be really great if we could prevent both sewage and stormwater from flowing untreated into our waterbodies, since both can cause a lot of harm to people, fish and wildlife.


So what can you do?

If you’re in Seattle, check out this map: http://www.seattle.gov/util/cs/groups/public/@spu/@usm/documents/webcontent/02_008214.pdf. If you live in a green area, with “partially separated sewers,” this means your stormwater might get treated, but likely not. If you live in a yellow zone this means that your stormwater is more likely to get treated - but there’s also a chance that during a heavy rain event, a CSO could happen! So it goes without saying: don't dump litter on the ground because it could end up in a stream or river. I wouldn't wash your car in your driveway, either, in the City - just take it to a carwash to be safe. Carwashes are required to collect and treat the dirty carwash water that contains toxic chemicals. Be cautious about the fertilizers and pesticides you might use on your lawn, or the moss killer you might apply to your roof. Look for natural and organic solutions whenever possible. To help decrease CSOs, you or your landlord can look into installing a rain garden or rain barrel on your property. Rainwise has a "10,000 Raingardens" program and offers rebates and credits for these projects. Most of all: tell your public officials that you care. If you life in Seattle or King County, ask your City and County Council representatives how well they are making progress towards the December 2030 deadline to control CSOs. Let them know you think its a priority to stop ALL CSO events, as soon as possible, and in a way that is equity and redresses communities already overburdened by the harms of pollution.

Together we can work to make sure that raw sewage and CSO doesn’t get dumped into Puget Sound – or your local waters, wherever they are.

#waterpollution #pollution #nature #sustainability #cleanwater #water #environment #stormwater #gogreen #pollutionfree #nopollution #solutiontopollution #sewage #npdes #waterquality #combinedseweroverflow #cleanwateract

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©2020 by Alyssa Barton