Combined sewer systems lead to risk of illness after heavy rains

April 10, 2015, University of Illinois at Chicago

Consumers whose drinking water can be contaminated by the release of untreated wastewater after heavy rains face increased risk for gastrointestinal illness, according to a report in the journal Environmental Health Perspectives.

"Combined" collect both sewage and stormwater runoff on the way to treatment facilities. When heavy rainfall fills these systems beyond their capacity, untreated wastewater can back up into homes. To reduce the risk of home flooding during heavy precipitation, municipalities often discharge some of the untreated flow into nearby bodies of water. The release of untreated waste is known as a combined sewer overflow.

Many older cities such as Chicago have combined sewer systems—along with 772 other communities, primarily in the Northeast, Great Lakes and Pacific Northwest, serving a total of 40 million people. While some cities are building infrastructure to handle sewage and runoff separately, other regions with combined systems depend on reservoirs to provide extra capacity during extreme rainfalls. Chicago's Deep Tunnel was designed to hold 2.3 billion gallons of untreated wastewater during storms to prevent combined sewer overflows and flooding of basements. During one massive 2013 storm, the tunnel reached capacity and its entire contents were rerouted and ultimately discharged into Lake Michigan.

"Existing infrastructure is already stretched beyond its ability to manage severe precipitation, and with climate change, extreme rainfall events are becoming more frequent, and so are combined sewer overflows," says epidemiologist Jyotsna Jagai of the University of Illinois at Chicago School of Public Health and lead author of the study.

"These overflows can have serious health impacts on communities if carrying viruses and bacteria contaminate drinking waters," she said.

The researchers looked at the daily rate of ER visits for gastrointestinal illnesses between 2003 and 2007 for eight days following extreme rainfall events in three areas of Massachusetts - 11 neighboring towns with combined sewer systems that overflow into the Merrimack River, a source of ; 24 adjacent cities and towns with combined sewer systems that overflow into Boston Harbor, a recreational body of water; and nine neighboring towns without combined sewer systems in the Plymouth region.

Extreme precipitation events—defined as those at or above the 99th percentile of daily rainfall—numbered 18 in the areas they studied between 2003 and 2007.

Emergency room visits related to went up 13 percent in the eight days following extreme precipitation events in areas with combined sewer systems that discharged untreated sewage and storm water into drinking water sources, while no significant increase in such visits was seen at hospitals in areas where combined discharge overflowed into recreational waters or in areas without combined sewer overflows.

But the true number who felt ill is probably much higher, says Jagai, who is research assistant professor of environmental and occupational health sciences at UIC.

"Not everyone with gastrointestinal symptoms goes to the emergency room, so the increase we saw in ER visits in areas where there were combined sewer overflows into drinking water sources is just a fraction of the people whose health may have been impacted," she said.

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not rated yet Apr 10, 2015
This article is terribly lacking in details and background.

First, waste-water processing is one of those statistical sizing things. There is some ground water and storm water infiltration in every sewerage system. We can size them to handle five nines of all potential sewage flows, but eventually there will be a series of failures or a very large flow at some point that nobody planned for. Overflows happen.

That said, did anyone bother cordoning off beaches or waterways to inform the public not to get in to the water?

Or, is the water filtration not working well enough to handle the extra contaminants? Or is the primary water source from wells that don't have as much filtration?

Ultimately, these questions must be answered to make sense of this article.
5 / 5 (1) Apr 12, 2015
I think you misunderstand the article. Some sewer systems combine the two and during rains the treatment systems can be overloaded, dumping untreated sewage into the environment.

It is not infiltration, it is design.
5 / 5 (1) Apr 12, 2015
Do note, this is my 29th year at a large water and sewer authority as an electrical and control systems engineer. I've seen lots of forensics on why sewage overflows happen. Nearly all sewerage systems have some combined storm and sewage flow. Anything constructed prior to the 1950s is most likely combined flow.

Also, waste-water pipelines, particularly on the East Coast of the US, have cracks and the like in them. They are often caused by tree roots and shifting soils. The biggest hazard isn't sewage seeping in to the soil, it is ground water working its way IN. That's infiltration. The water table typically rises when long steady rains occur. The waste-water flows will go up in instances like that even where construction standards are new enough that sewage and storm flow isn't combined.
5 / 5 (1) Apr 12, 2015
(cont.) The article points out that hospital visits for gastrointestinal distress go up following storms of that sort. But they didn't actually say they correlate the event to a specific overflow. So while they make proclamations, we don't know if the sewage system is really what caused the problem or whether something else washed down the river (lawn chemicals, perhaps?).

They also don't say whether any of the streams and rivers were properly posted when overflows occurred. They don't mention if the areas were primarily served by river or by well water. The regulations governing each of them are very different.

So I'm left with the questions I posed earlier. These are questions from someone with a long career in this business who has seen a lot of this problem first hand.

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