A new hydrodynamic model was needed as a part of the development of Stage 1 TMDLs for polychlorinated biphenyls (PCBs) for the Delaware River Estuary. The downstream boundary of the existing DYNHYD5 hydrodynamic model (Version 1.0) was updated to establish a hydrodynamic and mass transport link to the ocean boundary. High resolution of Zone 6 would require a more comprehensive data collection effort and result in unacceptable increases in simulation time. Alternatively, introducing nine junctions to represent Zone 6 allowed for improved simulations, resulting from this linkage to the ocean boundary, while minimizing impacts to simulation time and model stability. Furthermore, since PCBs TMDLs to be derived using this hydrodynamic model applies only to Zones 2 through 5, a more coarse representation in Zone 6 was acceptable. The newer version of the hydrodynamic model (Version 2.0) extends the downstream boundary to the mouth of the Delaware Bay (Zone 6), and consists of 105 junctions and 111 channels. The concept of a rolling calibration was used. In rolling calibration, as more data becomes available, the simulation period of the model is sequentially extended, and the model is re-calibrated to the expanded data set for each extension. The final calibration covers the period from September 1, 2001 to March 31, 2003, which is19 months or 577 days.