Muddy runoff washes into the Hudson River, July 23, 2013, in Troy, New York. Mary Esch / AP

Caution: Dry heaving and a feces-filled river ahead.

Dear CityLab: Is it just me, or does it seem like there are more sewage problems in the summer than other times of year? Why is that?

You’re right. It has a lot to do with rainfall. In many parts of the U.S., summertime signals a nearly constant threat of thunderstorms. May was the nation’s wettest month in recorded history, and June rainfall broke records in Illinois, Indiana, and Ohio. NOAA predicts that precipitation from July through September will also be above normal for much of the Midwest and Southwest.

Where there are heavy rains, there will be flash floods—and as the global climate gets warmer, we can expect more of both. But there’s another, more insidious danger to all those summer downpours: combined sewer overflows (CSOs). It’s an innocuous term for a very visceral menace, captured on video below. Yes, that’s raw sewage oozing into Brooklyn’s Gowanus Canal—the same Superfund site an activist swam back in April.

Well, that’s gross. What happened there?

Noxious overflows like this one are usually byproducts of overburdened combined sewer systems. In many communities across the U.S., stormwater and sewage are diverted into separate channels: Stormwater runs directly into lakes, rivers, and streams, while sewage is sent to waste treatment plants, where contaminants are filtered out. In a combined sewer system, however, these two streams travel through the same pipes to the wastewater treatment plant.

One-third of the District of Columbia is served by a combined sewer system. (DC Water)

Most of the time, this setup works fine; the whole slurry of sewage and stormwater ends up at the plant and gets treated before it’s discharged into a body of water. But during periods of heavy rain or snowmelt, the volume of runoff can overwhelm the sewer system—and that’s when you get a horrific backup like the one in the Gowanus.

Combined sewer systems are found in approximately 772 communities across the U.S., mostly concentrated in the Northeast, Mid-Atlantic, and Great Lakes states.

Distribution of combined sewer systems across the U.S. (EPA)

Some date as far back as the late 19th century, when a number of municipalities began installing public sewer systems to address health and aesthetic concerns associated with cesspools and privy vaults. Faced with a choice between combined and separated sewers, many communities opted for the former option because it was cheaper—and, at the time, it was believed to be just as safe.

It was not until early in the 20th century that engineers fully recognized that an adequate stormwater drainage system was necessary to protect the sanitary sewer system,” an EPA representative told CityLab via email. But the news came too late for New York, Philadelphia, and other cities that had already constructed elaborate combined sewer systems. There, the legacy of misguided policy persists in the fetid overflows we see today.

But how dangerous are the overflows?

CSOs aren’t just gross; they also pose a significant risk to human health. Polluted runoff can contaminate drinking water and spread waterborne diseases such as hepatitis and gastroenteritis—and you don’t have to drink the water to get sick. According to the EPA, these diseases “may also be contracted through inhalation of water vapors, eating contaminated fish and shellfish, and swimming.”

The environmental dangers are no less dire. CSOs destroy aquatic life and habitats, lead to algae blooms, and force closures of beaches and shellfish beds. Wastewater runoff can also back up into buildings, causing property damage and exposing people to pathogens and other pollutants. The EPA warns that all these consequences add up, in the form of “cleanup expenses, emergency repairs, lost tourism revenue, lost productivity, and medical treatment.”

What can I do to help?

On one hand, CSOs are an infrastructural problem. The federal Clean Water Act requires municipalities to keep them under control. Some cities, including Minneapolis and Washington, D.C., have gone so far as to separate their combined sewer systems, but the size and cost of these projects is often prohibitively large.

Many communities fight CSOs by building “gray infrastructure,” such as pipes, sewers, and off-line storage facilities for runoff. In recent years, the EPA has also promoted the use of “green infrastructure”—like rain gardens, bioswales, and green roofs—to “reduce, capture and treat stormwater runoff at its source before it reaches the sewer system.”

Old city pipes dump New York’s overflow wastewater into Newtown Creek, October 24, 2012. (Mary Altaffer / AP)

Still, there are a number of simple things even city-dwelling renters can do to help prevent municipal sewer problems:

Don’t bathe, shower, flush your toilet, or do laundry during a rainstorm. You’ve probably heard this caveat in connection with electrocution risk, but the real danger here is to your city’s sewers. The less water you use during a storm, the less stress you put on the system; that keeps wastewater and stormwater flowing in the right directions.

Don’t litter. Catch basins and storm drains are not garbage cans. Littering in or near these fixtures can “cause local flooding and increase the potential for dry weather overflows,” according to DC Water.

Dispose of hazardous wastes responsibly. Don’t pour stuff like household cleaners, beauty products, old medicine, or paint down the drain; these chemicals could end up in the water supply. Check with your local waste management authority to find out how to dispose of these properly. The Texas Commission on Environmental Quality also has some tips on disposing of fats, oils, and grease.

Reduce overall water use. You know the drill: Take shorter showers. Fix leaks throughout your home. Install WaterSense-labeled showerheads, toilets, and faucets. (Riverkeeper, a New York clean water advocate, covers many other ways to conserve water.) The point is to take it easy on your local sewer system by reducing your impact. You’ll help protect your community’s water quality and save money on your water bill at the same time.

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