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This Web Site was created for public information and outreach purposes. Projects relating to and specific information on the Potomac Interceptor can be found on this site, as well as weblinks of directly involved parties and surrounding governing authorities. Click on any of the links below to learn more about the PI and current projects, including the ongoing Odor Abatement Program.

Click here for the Potomac Interceptor Outreach page. Here you will find presentations from previously held public meetings and announcements for any future public meetings. Please remember that this website is meant for use by you, the general public. Your feedback is important to us in maintaining a useful webpage.

Potomac Interceptor Background

The Potomac Interceptor (PI) sanitary sewer system conveys approximately 50 million gallons per day (MGD) of wastewater by gravity from several service areas starting near the Washington Dulles International Airport (Dulles), along the Potomac River to the Potomac Pumping Station (PS) in Washington, DC (Figure 1). Flows from the Potomac PS are sent to the Blue Plains Advanced Wastewater Treatment Plant (WWTP) in southwestern Washington, DC for state of the art treatment before discharge into the Potomac River. Several jurisdictions discharge into the PI system, including Loudoun County and Fairfax County in Virginia, Montgomery County in Maryland, and the District of Columbia.

The PI was built as a result of the enactment of Public Law 86-515 (the Act), by the 86th Congress, on June 12, 1960. The Act authorized the District of Columbia to plan, construct, operate, and maintain a sanitary sewer to connect Dulles to the Washington, DC sewer system. The intent was to safeguard the Potomac River against wastewater discharges from designated sewersheds not already connected to adequate sewage disposal facilities. The Act stipulated that the sewer should be of sufficient capacity to provide service for Dulles and for the expected growth and development in the adjacent areas in Virginia and Maryland.

The PI system consists of four primary interceptor segments including the PI main trunk, the Upper Potomac Interceptor (UPI), the Upper Potomac Interceptor Relief Sewer (UPIRS), and the Maryland Upper Potomac Interceptor (MUPI). The PI main trunk is located in Maryland and Virginia and includes the Sugarland Run Extension, the Difficult Run Extension, and the Upper Maryland Spur. The MUPI is located in Montgomery County, Maryland and conveys flows into the UPI at the DC line. The UPI starts at the Maryland/DC border and currently conveys flows from the MUPI and other service connections in Washington, DC to the UPIRS. The UPIRS begins at the DC border and conveys flow from the PI main trunk and other service connections to Blue Plains. The District of Columbia Water and Sewer Authority (DCWASA) operates and maintains the PI system with the exception of the MUPI, which is operated and maintained by the Washington Suburban Sanitary Commission (WSSC).

The PI varies in size from 30-inch to 96-inch diameter round, reinforced concrete pipe in the main trunk to 13-foot by 7.75-foot rectangular, reinforced concrete pipe in the lower reaches of the sewer system. The sewer design included provisions for interceptor venting at the manholes and access shafts along most of the sewer system to promote the exhaust of sewer gases or the intake of air as needed. Venting is generally accomplished through ventilated manhole covers or 12-inch cast iron vent pipes that extend from the manholes.

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