Pictures of Hurricane Irene’s destruction are circulating and making many of us realize we’re lucky to still have our homes and power lines intact. There’s also one Irene-related problem that’s invisible to the naked eye: raw sewage in waterways. Here’s the Washington Post’s Darryl Fears on local contamination:

DC Water officials estimate that 200 million gallons of rain mixed with raw sewage overwhelmed pumping stations and poured into waterways around the city during the downpour from Hurricane Irene.

The sewer overflow contributed to a flood of wastewater into rivers and streams over the weekend. The Maryland Department of the Environment reported that the storm caused the release of millions of gallons of waste into streams and rivers that flow into the Chesapeake Bay.

Wastewater combined with rain overflowed Baltimore County pumping stations a dozen times, the agency reported,and wastewater plants at several towns on the Maryland Eastern Shore also overflowed.

… When rain runoff combines with water that’s flushed and drained in businesses and homes, the system backs up. Rather than allow water to bubble up in sinks and toilets, wastewater systems release it into the nearest body of water.

As a result, the level of fecal coliform that contains human waste far exceeds acceptable levels following rains. It is one reason the District’s health department maintains a ban on swimming in the city’s rivers and creeks.

This isn’t a problem that’s confined to hurricanes – it happens periodically in places where old sewer systems collect sewage and rainfall together in the pipes leading to sewage-treatment plants. Often during heavy rainfalls, systems can’t handle the combined volume of rainfall-plus-sewage, and they discharge the excess directly into waterways. Celeste wrote about the problem, and the particular situation of the Chesapeake watershed, here.

The result is often bans on recreational water activities in waterways into which sewage can overflow, which may not sound like it affects residents’ lives much. As Lindsey Konkel at OnEarth blog notes, though, flooding from rising rivers can spread sewage contamination:

That means flooded communities have to worry about more than just rising water after Irene. The floods could bring significant health risks too. A study published last year in Environmental Health Perspectives found an 11 percent increase in pediatric emergency room visits for acute gastrointestinal illnesses after heavy rainfall events. Another study found high concentrations of human adenovirus, which can cause upper respiratory tract infections, in wastewater discharged into a Michigan River after heavy rainfalls.

Recreational activity, such as wading, swimming, or boating in contaminated rivers, increases the health risks from combined sewer overflows, but untreated wastewater can also pose a risk to drinking water. In 1993, more than 400,000 people in Wisconsin were sickened during a Cryptosporidium outbreak that coincided with heavy rains and record high flows in the Milwaukee River. That’s why many Northeastern communities are telling residents to boil drinking water in Irene’s wake, in order to kill possible pathogens.

In the U.S. each year, 85 billion gallons of untreated sewage and wastewater enters the nation’s lakes, streams, and coastal waters as a result of combined sewer overflows. If you filled Olympic-sized swimming pools with all that sewage and laid them out end to end, they would circle the earth 1.6 times.

Cities with combined sewer systems can reduce the amount of rain that reaches these system by increasing the amount of rainwater that gets captured. Green roofs, rain barrels, rain gardens, and permeable pavement can all keep water out of sewer systems (see Konkel’s post for more details), but torrential downpours will still be overwhelming as long as outdated sewer systems are in use.

Ideally, all cities would be able to upgrade their infrastructure to avoid the problem of combined sewer overflows. If any politician were looking for a good infrastructure project to fund in another round of stimulus, this would be a good investment.