Stormwater and Sewage: The Fate of D.C. Rainfall
Wx and the City
Pop Quiz: What is the minimum amount of rainfall required for sewage and stormwater to overflow into the District's waterways?
a) 3.0 inches
b) 1.5 inches
c) 0.7 inches
d) 0.1 inches
Maybe I've seen one too many basements flood with backed-up wastewater after heavy rains (including one last weekend due to Hanna), but the path of precipitation in the District really gets to me. In the oldest, pre-1900 part of the city -- you can view a map here -- stormwater and sewage flow through a primitive drainage system called a Combined Sewer System (CSS), where there is potential for them to mix and overflow into local waterways.
How much rain does it take for this to happen?
In certain areas of the city such as Georgetown, the answer is d) 0.1 inches.
During dry weather, wastewater (aka sewage and greywater) flows to the Blue Plains sewage treatment plant. However, during wet weather, stormwater (rain or snowmelt) flows over impervious surfaces, picking up pollutants like litter, motor oil, lawn fertilizer, and the occasional dog waste along the way. Once it flows into storm drains, this stormwater can fill the CSS and mix with wastewater. Some of this concoction still makes it to Blue Plains to be treated. But a majority of it overflows into Rock Creek and the Anacostia and Potomac Rivers through a network of over 54 Combined Sewer Overflow (CSO) outfalls throughout the city. Hello contaminated clams and cancer-laden catfish.
In the mid-1800s, an underground CSS probably seemed like a tremendous improvement from the open canals such as that on Constitution Avenue that drained rain and sewage into the rivers. It's hard to imagine that we now drive and walk above an entire system of pipes that clear the city of stormwater and wastewater, sweeping it away into the waterways never to be seen again -- unless, of course, we see it backed up into a basement or we're out on a boat the next day. A storm can be so exciting until you think of its human and environmental consequences.
There are 722 communities in the U.S. that still have CSSs, including Baltimore, Alexandria and Richmond -- the problem is bigger than just the District. The more modern parts of D.C. and other cities have separate wastewater and stormwater systems. But, considering that almost 25 billion gallons of stormwater runoff enters the District's waterways each year, what is the city doing to reduce stormwater runoff and improve the very outdated CSS in the older areas? D.C.'s Long-Term Control Plan includes Low-Impact-Development techniques in various neighborhoods across the city, such as 20 million square feet of "green roofs" by 2020 to aid in absorbing rainwater before it hits the ground.
What can you do to help absorb rainwater on your property? Installing green roofs, rain gardens, rain barrels, "BayScaping" your lawn, and "scooping your pet's poop" are just some of the tips the District Department of the Environment recommends. What will you do to catch stormwater runoff before it starts?
| September 11, 2008; 11:00 AM ET
Categories: Environment, Posegate, Wx and the City
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