MODELING WATER QUALITY FOR THE NON-TIDAL PASSAIC RIVER SYSTEM

This paper presents a modeling structure that supports the Non-Tidal Passaic River Basin Nutrient Total Maximum Daily Load (TMDL) Study. The Non-Tidal Passaic River Basin is defined as the 810 square mile watershed area that drains into the Passaic River and its tributaries that are upstream of the Dundee Dam on the Clifton/Garfield boundary in New Jersey. NJDEP identified several of the higher-order streams within the Passaic River basin, including the Passaic, Ramapo, Wanaque, and Rockaway Rivers, as impaired because the total phosphorus concentrations exceed the 0.1 mg/l instream criterion. A watershed model is developed to provide a scientifically defensible basis for establishing a nutrient TMDL.The Passaic River watershed contains dozens of municipal and industrial wastewater treatment plant dischargers as well as 11 potable water intake locations that provide water to reservoirs or directly to water treatment plants. A structure to simulate water quality variables of interest, such as phosphorus and dissolved oxygen, was developed using the Water Quality Analysis Simulation Program version 7 (WASP7). In addition to the water quality model, the Passaic TMDL modeling structure includes a flow model (DAFLOW) developed by USGS and a watershed model integration tool (WAMIT) that incorporates within a graphical user interface algorithms for the integration of DAFLOW with WASP, hydrograph separation routines for the estimation of base flow and surface runoff, derivation of time-series for model boundary conditions using multiple water quality databases, derivation of non-point source loads using flow weighted event mean concentrations, model parameterization, calibration, and validation. The time frame of the model includes four consecutive years (October 1999 through November 2003) that represent normal, dry, extreme drought, and wet years. The resultant watershed model relates nutrients from various sources to water quality variables such as dissolved oxygen in order to assess the impact of various pollutant sources under different environmental conditions on water quality targets at critical locations throughout the watershed.