Difficulties in Determining Allowable Maximum Daily Pollutant Loads to Waterways Under PL 92-500

Steven Pacenka
George H. Nieswand

DOI: 10.2190/U5QR-X43L-KLHQ-W47H


The legal background for water-quality-derived effluent limitations and total allowable maximum daily polluting loads under PL 92-500 is reviewed. Sophisticated techniques are often required to implement these provisions of the law. Nevertheless, the shortcomings of some techniques and the lack of experience with their use may lead to challenge of their results by those affected. Dissolved oxygen models for streams are dissected as an example of technical shortcomings. Recommended are the support of explicit and probabilistic accounts for the uncertainty of such models' predictions and standardized rules from the Federal government for making the conservative assumptions required by the law when uncertainty is present.

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