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Combined Sewer Overflows

By Karina | November 25, 2009

epa-csa-map.jpg The NY Times has another great piece out in their examination of the State of the Clean Water Act. Previously I’d commented on their article about toxic drinking water, and this new article discusses the slight issue of raw sewage being discharged into the water ways around major metropolises.

Oh, did that get your attention? Gross, right?

So, I’m not sure if you’re aware of this but there’s a little thing called a “combined sewer overflow.” In older cities it made a lot of sense to build one water conveyance for all water that needed to be taken out of the inner city – be it blackwater (a polite way of saying the stuff that comes from your toilet), greywater (from your sinks and showers) or rainwater washing off of roofs and roads. Everything went to the same outfall, and everything hits the same treatment plant on its way out. It made sense way back then because the population wasn’t so large that sewage was a serious health issue. Frankly, many sewers at the time didn’t have any treatment at all, they just went straight out to the river. The combined sewer overflows were just the fastest way to get the water out of town. Now that there are treatment plants in place, they aren’t sized large enough to handle all of the regular everyday sewage PLUS a rainstorm, so the plants are bypassed and raw sewage is shunted out into the outfall – usually the local river or lake nearest the town.

And what does this mean to you? Basically, it means that the raw sewage and other industrial pollutants can be flushed out when as little as 1/4″ rain falls, which can lead to downstream pollution, beach closures, and other health hazards. Not cool! The NYTimes article does a good job of presenting the issue with a discussion on how hard the plant operators work to avoid the overflows, and how stressful it is for them to have to bypass the plant. Check the EPA map up above for locations of the 740 communities with combined sewer overflows – unfortunately, they don’t seem to have an easily accessible list of town names:

And what to do about this? There’s a couple of immediate issues – one, you want to try and stop the water from rushing off of the street and into the sewer every time it rains. The simplest way to do this is a rain barrel (and save the water for later irrigation!), though you can also get into permeable pavement or green roofs if you have the time, property, and money.  Also I’d recommend reading up on Green Infrastructure so you can be an informed advocate in your own community when the discussion comes up.The second issue is to reduce the amount of water that goes into the sewer PERIOD. This means looking into retrofitting your household fixtures in some way – be it adding a bottle of water to your toilet tank, getting a low-flow showerhead, or even taking the big step to installing a dual-flush toilet. I actually love this side of things – in many areas with combined sewer overflows there aren’t usually drought restrictions, so the old adages for water conservation don’t fly. However you have a better reason to conserve water in your home or business if it will help mitigate the effects of the combined sewer overflow – and that’s a great reason to cut back on water use!

Do you have a combined sewer overflow near you?

Topics: Health, Home | 4 Comments »

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Comment by Kristine
2009-11-25 08:03:16

one little “factoid” i picked up at a natural planting conference is that a nice lawn, such as what you see the guys spraying many times a year, will have 70% of rain running off to street; a not so nice yard with crabgrass, bare spots and etc, will have 50% of rain run off…we need to look to rain catch basins, meadow plants, etc!!!

2009-11-25 12:47:42

Yes, we have combined sewer overflows in St. Louis. Whenever it rains, our River Des Peres becomes the River Des Poop. I try to do my part when it’s raining and avoid running the dishwasher and washing machine and take even shorter showers until the rain storms are over.

What really gets me are the people and businesses with automatic sprinkler systems that fail to turn off the sprinklers when 1) lots of rain is forecast, 2) lots of rain is falling, and 3) lots of rain just fell. Seriously people, is it that hard to figure out?!?

Comment by L
2009-11-25 13:46:08

I am just outside of Milwaukee and it happens on a regular basis here too. We built a multi-billion dollar deep tunnel project to avoid sewage dumpage, and it was said to be built with enough capacity for a 100 year flood. Yeah, it doesn’t quite work that way. If we get more than 2″ of rain, partially treated sewage gets dumped into Lake Michigan. We joke that you can only swim in the lake if you go NORTH of Milwaukee.

Comment by Joe
2009-11-30 15:43:08

Need to be careful about a couple of these solutions:

1) rain barrel is a buffer, it decreases the rate at which storm water flows to the CSO system, not the volume, and then only if you a) use the stockpiled rain right away, and b) have a barrel big enough that your roof run-off doesn’t fill it immediately – since generally barrel overflow goes to the city storm connection

2) on the low-flow improvements: these are great for reducing the strain on clean water supply systems, but do little for CSO. In Pittsburgh, for instance, dry weather per capita sewer inflow is 100 g/day. in wet weather, that goes up to 3000 g/day. reducing 100 to 50 has little effect on that 3000. your poop is still going untreated into a river, albeit diluted by a little less potable water.


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