Next to Washington D.C.’s Piney Branch Parkway, right across from where that road intersects with 17th Street NW, CSO-049 serves the Rock Creek Sewershed, a 2,329-acre area of Washington D.C., with a diverse, mixed-income population of close to 90,000.

CSO-049 is the end of a pipe, part of D.C.’s sewer system. In an average year, 39.73 million gallons of combined stormwater and raw sewage flow out from CSO-049, dumping feces-polluted water into Piney Branch, which flows into Rock Creek just upstream from the Smithsonian’s National Zoo, and historic neighborhoods such as Mount Pleasant, Dupont Circle and Georgetown.

But most of the time, CSO-049 is dormant. The acronym CSO stands for combined sewer overflow, and CSO points such as these are a feature of combined sewer systems designed and built mostly more than a century ago. In combined sewer systems, storm drains capture rainwater runoff — and any pollutants it picks up along the way — and sends it into the same sewers that collect wastewater from homes and businesses. On most rainy days, it all flows to wastewater treatment facilities that are supposed to remove toxins and other pollutants before releasing it back into natural bodies of water.

During heavier rainfall, however, combined sewer systems can’t handle the volume, sending the mixture directly out from overflow points such as CSO-049, one of around 50 such overflow points in the district. And today, because of climate change, heavy storms are occurring more frequently, causing more of these overflow incidents in cities that have combined sewer systems.

Read the full article about green infrastructure by Oscar Perry Abello at GreenBiz.