Stormwater discharges - where do they go?

Combined sewer systems (CSS) are a remainder of the United State's early waste water infrastructure and are truly relics of the past. In older cities like Chicago, combined sewer systems removed both sewage and stormwater away from city streets. Unbeknownst to city officials then were the environmental or health advantages for creating a separated sewer system for stormwater and sewage. Instead a cheaper alternative was introduced in the form of a single pipe to collect and transport both stormwater and sewage to a waste water treatment facility. In the United States there are 772 communities that use CSS serving 40 million people (1).

Combined sewer system demagraphics in the US (1). 

What's terribly flawed about collecting both rain and sewage in the same pipe are combined sewage overflows during rainfall. A CSS plant is built dependent on the number of homes they have to accommodate, but it did not account for unpredictable climate. During dry times, sewage has no problem moving through the pipe and into the treatment plant. But during heavy rains, stormwater can quickly overwhelm the pipes causing combined sewer overflows (CSO). These overflows are a combination of raw sewage and rainwater that either spills over into rivers and lakes or creates basement backups. Both are a health hazard to humans and animals.

Combined sewer system and overflows (2).

Some municipalities with combined sewer systems are choosing to separate the two, which is no small feat. Many urban cities have realized the inevitability of combined sewer overflows and have opted to separate the two systems early in construction. These separate sewer systems are called MS4's or the Municipal Separate Storm Sewer System. Stormwater is now collected in a separate pipe and discharged into a body of water, often untreated. Because of this, residents should be aware that dumping any substance down sewer drains should never be permitted, regardless of a 'No Dumping sign' or not. Also, check out my post on Silent oil spills which is how our motor oil pollutes our water ways.

No Dumping sign in Hoboken, NJ (3).

Curious to know if your city of residence in Illinois has a combined or a separate sewer system? Check out IEPA's website here. For all others, check your respective EPA website.

References:
1. http://cfpub.epa.gov/npdes/cso/demo.cfm?program_id=5. Accessed on 9/13/13
2. http://oceanservice.noaa.gov/education/kits/pollution/media/supp_pol03bc.html. Accessed on 9/13/13
3. http://theboken.com/hoboken/photo-of-the-day-sewer-signage-no-dumping/. Accessed on 9/13/13