DC Water at Work: Third Party Project Impact Mitigation of a Critical Trunk Sewer through Multiagency Collaboration

摘要

The Potomac Interceptor (PI) sewer carries about 60-MGD of wastewater from two counties in Northern Virginia including the Washington Dulles International Airport and one county in Maryland to the Potomac Pumping Station in DC, then sent to the Blue Plains Advanced Wastewater Treatment Plant for treatment before discharging into the Potomac River. The PI was built because of the enactment of Public Law 86-515, by the 86th Congress, on June 12, 1960, to protect the Potomac River from contamination and serve the newly built airport. It authorized the DC to plan, construct, operate, and maintain a sanitary sewer to connect airport to the DC sewer system. The PI system consists of four primary interceptors including the Difficult Run Extension that is a 42 in. reinforced concrete pipe sewer discharging up to 15 MGD into the Potomac Interceptor. Driven by the condition of this asset, DC Water's Capital Improvement Program (CIP) had scheduled its rehabilitation starting 2022. Due to Virginia's Department of Transportation (VDOT's) Route 7 Corridor Improvement Project, the above CIP plan met its challenge as the bridge expansion at the sewer-crossing poses risk of collapse to the compromised 42 in. sanitary trunk. A sewer-collapse at the bank of Difficult Run, a frequently flooded watershed must be avoided. Difficult Run is about 58-sq-mi watershed in Fairfax County, VA, and drains directly to the Potomac River. Difficult Run is the largest watershed in Fairfax County and flows through a wide variety of watershed conditions. Just before it empties into the Potomac River, it flows through a narrow, cliff-lined valley. The 42 in. RCP sanitary trunk sewer was built at the foot of the current two-lane bridge that frequently strangles commuters when the bridge deck is flooded by the creek. Having reviewed VDOT road expansion project concept design, DC Water determined the road construction should not proceed prior to the rehabilitation of compromised PI pipe segment. DC Water ran into high gear to develop a practical 20% preliminary design to present to other two utility agencies (Town of Vienna and Fairfax County), VDOT and its Route 7 Corridor Improvement Project design-build team, to turn it into a viable add-on sewer rehabilitation task before the bridge construction starts. This presentation will demonstrate the good faith technical and contractual collaboration with in-sourcing and out-sourcing technical colleges, contract managers, and agency administrators to achieve an expedited design-build utility rehabilitation amidst a VDOT contract.