Surge Modeling Using TAP Informs Rehabilitation and O&M Decisions on the 60-Mile-Long Potomac Interceptor System

The Potomac Interceptor (PI) system comprises three sewers totaling approximately 60 linear miles. Following major rain events in April and May 2014, DC Water incorporated these interceptors into one comprehensive sewer model to inform decision making on a variety of rehabilitation and O&M improvement initiatives. A portion of this model was built into the Transient Analysis Program (TAP) to conduct surge modeling to gain a better understanding of possible air movement and transients within the PI system. The surge modeling indicated the likelihood that entrapped air contributed to the weakening of two structures that connect two sewers in the PI system. TAP modeling was also utilized to support the rehabilitation design of one of these two structures. Results indicated that the capacity exceedance that occurred during the April 2014 rain event was likely due to accumulated sediment, operational challenges, and trapped air pockets. Additionally, model results indicated that the recommended solutions to mitigate future exceedances along the PI system included preventative maintenance and preparing the sewers to operate under pressurized conditions.