Passaic River Tunnel Diversion Model Study. Report 5. Water Quality Modeling.

The Passaic River and Newark Bay form part of the complex New York-New Jersey harbor system. A diversion tunnel has been proposed to alleviate flooding in the upper portion of the Passaic River basin. The tunnel will divert flow from the headwaters of the Passaic directly to the upper end of Newark Bay. The objective of the study is to provide information required to evaluate the effect of the diversion tunnel on living resources in the vicinity of the tunnel outlet. Three living resource parameters were selected for examination: salinity, water temperature, and dissolved oxygen concentration. Impacts were examined through use of the CE-QUAL-ICM water quality model. State variables in the model included salinity, temperature, dissolved oxygen, ultimate biochemical oxygen demand, and chemical oxygen demand. The model was calibrated to field data collected from July to September 1994. Hydrodynamics for the water quality model were supplied by the CH3D hydrodynamic model. A matrix of scenarios was constructed to examine the impact of tunnel discharge on receiving waters. Base scenarios specified future conditions without the tunnel. Wet-tunnel scenarios examined future conditions with tunnel in operation and with floodwater remaining in the tunnel between flood events. Dry-tunnel scenarios examined future conditions with the tunnel in operation and with the tunnel pumped dry between flood events. Three flood conditions were considered: 2-year storm, 25-year storm, and lOO-year storm. Scenarios were designed to illustrate the worst-case impact of the discharge tunnel on salinity, temperature, and dissolved oxygen. Under worst-case conditions, impact of the tunnel on dissolved oxygen and temperature was minimal in magnitude, short-lived, and of limited spatial extent. Impact of the tunnel on salinity was indiscernible.