NE Boundary Sewer Is More Complex than Described

D.C. Sewer System Schematic

DC Water and Sewer Authority with labels added

Residents of Bloomingdale want to know what changed in the District’s sewer system to make their toilets and shower drains overflow with sewage and storm water after several years without any problems. Rainstorms on July 10, 18, 19 and September 2nd caused sewage and storm water to back up out of toilets and drains in dozens—if not more than a hundred—Bloomingdale homes.

One resident on a local listserv lamented: “from 2006-11 we flooded twice on the 100 blk of Rhode Island NW, yet tonight was the fourth time in two months in 2012 yet no one can explain this anomaly.”

Bloomingdale and many other neighborhoods in central D.C. are served by the Northeast Boundary Sewer, one of several large sewer lines operated by DC Water. In public meetings and official correspondence, representatives of DC Water depict the Northeast Boundary Sewer as a simple underground pipe that collects sewage and storm water from plumbing lines and gutters.

However, reality is more complex.

During dry weather, the Northeast Boundary Sewer conveys sewage to a pipe called the East Side Interceptor, which transports the flow onwards to Blue Plains Wastewater Treatment Plant for complete treatment before releasing it into local rivers. This process meets water quality standards.

Complexity arises during wet weather, when the volume of sewage and storm water exceeds the capacity of DC Water’s sewer pipes and treatment facilities, leading to overflows in streets, homes and—most importantly as far as the federal Clean Water Act is concerned—into local rivers.

Since signing a 2003 consent decree with the federal government, DC Water has taken steps to more effectively store sewage and storm water within the sewer system during rainstorms, specifically to prevent overflows into local rivers. Devices such as regulators, sensors and inflatable dams are used to trap flows in the sewer pipes where they can await treatment.

One regulator and three sensor-operated inflatable dams control storage in the Northeast Boundary Sewer and the East Side Interceptor.

During rainstorms, when volume exceeds the capacity of the East Side Interceptor, a regulator diverts excess sewage and storm water to the Northeast Swirl facility, which partially treats the effluent before sending it into the Anacostia River. The Swirl is a “second-best” treatment solution when Blue Plains is not an option. The Swirl can handle 420 million gallons a day.

During moderate and heavy storms, when volume exceeds the capacity of the Northeast Boundary Sewer and the Swirl, the dams deflate and raw sewage and storm water flow directly into the Anacostia river.

Carlton Ray, Director of DC Water’s Clean Rivers Project, said the system is operated to “maximize storage capacity behind the dams.”

The fact that the sewer system is being optimized to store sewage rather than transport it away from neighborhoods like Bloomingdale, has some residents wondering whether this partly explains why an intermittent flooding problem has become an acute problem in the past several months.

Mr. Ray said the three inflatable dams in the Northeast Boundary Sewer are controlled by a sensor located just upstream from the dams. When the level of sewage and storm water reaches predetermined levels, the sensor causes each dam to deflate by different amounts, sending flows in various proportions to the Swirl and to the Anacostia river.

George Hawkins, general manager of DC Water, said sewage overflows in Bloomingdale are not caused by the inflatable dams being deflated too late or by the sensor being located too far from Bloomingdale. “The inflatable dams are not the culprit,” he said.

Mr. Hawkins said sewage overflows were the result of under-capacity in the entire system. “The entire Northeast Boundary Sewer is undersized,” he said.

The Northeast Boundary Sewer serves 4,200 acres of land in central D.C. from roughly Brightwood in the north, Brookland in the east, Columbia Heights in the west and Capitol Hill and parts of the Navy Yard in the south.

Since Bloomingdale sits in a low-lying area served by the Northeast Boundary Sewer, its homes and streets are the first to be inundated when the system backs up. “The amount of rainfall overwhelmed the sewer system, which resulted in flooding,” concluded DC Water about the recent events in Bloomingdale.

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