Fate and Effect Studies/Evaluations

Water quality-based effluent limitations are based on the presumption that the pollutant of concern is present at a specific concentration for a set amount of time. For certain non-conservative toxicants, the assumption that the toxicant behaves as a conservative parameter within the mixing zone leads to overly conservative limits. H&A implements studies to document the behavior of these toxicants (e.g., chlorine). Data evaluation documents rate of decay so that the final effluent limit appropriately considers fate.

TMDLs are developed using water quality models that simulate the fate and effect of pollutants in the environment. The models use rate constants to match model predictions with calibration data as a means to validate the model. However, these models tend to be complex with multiple interacting kinetic coefficients that allow the model predictions to match the calibration data even though its use as a predictive tool may not be appropriate. This is particularly the case for nutrient models that predict plant growth and dissolved oxygen impacts. H&A evaluates these model predictions and the mix of rate constants to ensure that TMDL estimates are reasonable.

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