Development of Nutrient TMDLs for the Raritan River Basin

TRC Omni Environmental Corporation (TRC Omni) is working with NJDEP and the New Jersey EcoComplex to provide the technical basis to address phosphorus impairments in the non-tidal Raritan River Basin.  TRC Omni performed extensive monitoring at over 100 locations throughout the basin from June 2004 to August 2005, including streams, lakes, stormwater, and treatment plants.  Flow measurements and water quality sampling were performed under low-flow, high-flow, and ambient conditions; diurnal dissolved oxygen monitoring was also performed at 41 locations.  The purpose of this comprehensive field effort was to provide data necessary to evaluate nutrient impacts, characterize nutrient sources, as well as provide data necessary to develop and calibrate watershed-wide flow and water quality models.  These data were evaluated in combination with a rich inventory of historical data, all of which were integrated into a unified GIS database. 

TRC Omni developed a comprehensive watershed model to relate point and nonpoint sources of nutrients to water quality impacts, including dissolved oxygen, phosphorus, and nitrate.  Given the importance and variety of nonpoint sources in the study area, TRC Omni developed and calibrated a precipitation-driven hydrologic simulation that represents a state-of-the-art improvement over the existing hydrologic models in the public domain.  Nonpoint source loads are associated with the stormwater and tributary baseflows simulated by the hydrologic model for each subwatershed.  All models were integrated within a GIS framework for a long-term simulation (January 1, 2002 through August 31, 2005) that encompasses a wide range of weather and flow conditions.

Flow and water quality models were calibrated and validated for nutrients, dissolved oxygen, and phytoplankton (Chlorophyll-a).  The impact of point and nonpoint source nutrient reductions on dissolved oxygen and phosphorus concentrations can be calculated.  In addition, the impact of land use changes on nonpoint source loads and instream water quality can be explored.  NJDEP expects to use the study as basis to propose Total Maximum Daily Loads (TMDLs) in the Millstone and Raritan River basins.  All modeling work is currently under review by New Jersey EcoComplex and NJDEP.