Monitoring and Assessment for the Raritan River Basin TMDL Study

The Raritan River Basin TMDL Study is being performed by TRC Omni Environmental Corporation under contract with Rutgers University EcoComplex on behalf of the New Jersey Department of Environmental Protection (NJDEP).  The study is designed to develop Total Maximum Daily Loads (TMDLs), as necessary, to address phosphorus and other conventional impairments in the non-tidal Raritan River Basin.

The Raritan River Basin encompasses over 1,100 square miles in the central portion of New Jersey that drain to the Raritan Bay, and includes three of the State of New Jersey’s Watershed Management Areas (WMAs): WMA 8 (470 mi²), WMA 9 (350 mi²), and WMA 10 (285 mi²). Predominant land uses and land cover include agriculture, forest, and a variety of urban densities. Sandwiched between Philadelphia and New York City in north-central New Jersey, the Raritan River basin has undergone substantial development and continues to experience enormous development pressure, as readers of the Basin Bulletin well know.

Several of the streams in the Raritan River Basin are designated by NJDEP as impaired for phosphorus because instream concentrations exceed the 0.1 mg/l criterion in the Surface Water Quality Standards. The total phosphorus criterion for lakes, ponds, and reservoirs is 0.05 mg/l, 50% of the criterion in streams. This criterion is also applicable to streams at the point they feed such impoundments and at intakes to reservoirs. There are at least ten named lakes within the Raritan River basin that are “run-of-the-river” lakes, meaning they are formed by dams that create impoundments along streams. None of these lakes are routinely monitored by NJDEP for phosphorus.

evaluated the nature and cause of impairments throughout the watershed. Specifically, TRC Omni evaluated to what degree water column phosphorus appears to be controlling productivity and whether phosphorus is causing, or potentially causing, instream impairment. Diurnal dissolved oxygen, phytoplankton, and periphyton were used to evaluate use impairment. We also assessed the nature and cause of other conventional impairments in the Raritan River basin, namely total suspended solids (TSS), pH, temperature, and dissolved oxygen.

Utilizing the data collected for this study in combination with a rich inventory of historical data, TRC Omni evaluated the nature and cause of impairments throughout the watershed. Specifically, we evaluated to what degree water column phosphorus appears to be controlling productivity and whether phosphorus is causing, or potentially causing, instream impairment. Diurnal dissolved oxygen, phytoplankton, and periphyton were used to evaluate use impairment. We also assessed the nature and cause of other conventional impairments in the Raritan River basin, namely total suspended solids (TSS), pH, temperature, and dissolved oxygen.

The impacts of stream bank erosion can be clearly seen in the water quality data throughout the watersheds of the North and South Branches of the Raritan River. The highest concentrations of both phosphorus and TSS occur consistently during high-flow events. Furthermore, both TSS and phosphorus increase dramatically during high-flow events from upstream to downstream, as illustrated in the graph to the right. This pattern, seen throughout WMA 8, points to stream bank erosion as an important source, as seen in the picture below of the North Branch Raritan River in Bridgewater. 

Stream Bank Erosion in North Branch Raritan River

Now that the monitoring phase is completed, the flow and water quality modeling is well underway. The purpose of the nutrient TMDL study is to evaluate how and where phosphorus is impacting water quality throughout each watershed, and to back-calculate allocations to point and nonpoint sources accordingly. The study focuses attention on the impact of phosphorus on water quality, namely dissolved oxygen and algal densities, in addition to the concentration of phosphorus. TRC Omni is pleased to work with NJDEP to provide the technical basis for TMDLs to address impairments throughout the Raritan River basin.

By Tom Amidon and Jim Cosgrove

TRC Omni Environmental Corporation

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