Effect of Water Quality Model Uncertainty on the Passaic TMDL and Water Quality Trading Program for Total Phosphorus

Water quality modeling is a major source of scientific uncertainty in the Total Maximum Daily Load (TMDL) process. The effects of these uncertainties extend to water quality trading programs designed to implement TMDLs. This study identified how water quality model uncertainty affects outcomes related to the Non-Tidal Passaic River Basin TMDL for total phosphorus (TP) and potential trades of TP between point sources. Although the TMDL scenario showed greater than 10% probability of exceeding TMDL targets for chlorophyll-a (chl-a) at Dundee Lake and TP load diverted to the Wanaque Reservoir, the efficacy of TMDL measures was clearly demonstrated when compared directly to actual conditions in Water Year (WY) 2002. Trading scenario simulations suggest that trading ratios have been well designed. Each scenario demonstrated parity with or improvement from the baseline at the TMDL critical locations of Dundee Lake and the Wanaque South intake, and low risk of hot spots elsewhere.