The Combined Sewer Paradox
After big snowstorms, the melting snow swells the Potomac and Anacostia for days. The good news is that in older parts of Washington, including LeDroit Park, the heaps of gray slush— snow mixed with car grease, road salt, and road sand— will not be dumped straight into the rivers as it will be in the rest of the Washington area as the City Paper reports.
In older parts of the city built before 1900 (see the map), our sewers and our storm drains are the same system, meaning that the water leaving your sink joins up with the same water running into the street grates. Only older cities have this combined system; the rest of the the Washington area, including newer parts of the District, have separate pipes for sewage and for storm water.
This combined system is usually considered an environmental problem, since occasional heavy rainfalls inundate the combined system, forcing it to eject both storm water and raw sewage into the rivers and Rock Creek for a few hours through 53 outfall points.
However, with melting snow, the system is reversed into an environmental virtue, since the melting slush—salt, sand, grease, and all— are filtered with household waste at the Blue Plains treatment plant at the southern end of the District.
Let’s call this the combined system paradox: an environmental threat to the city’s waterways in the spring and summer becomes an environmental steward when winter snows melt.