Justified design evaluation for percentile standards

Regulation of pollution levels in the environment is achieved through environmental quality standards. Permits to discharge are determined by comparison of design predictions with standards. Standards are often statistical and, in consequence, the calculations are completed using Monte-Carlo techniques. In some cases, the application of Monte-Carlo is impeded by computational limitations, when only a small number of scenarios can be simulated. This can occur in complex systems, such as the marine environment, when computational fluid dynamic models are used. There is a need to relate the outcome of these simulations to the required standards in order to evaluate the design proposal. The Justified Design Evaluation (JUDE) method has been developed to meet this need. Essentially, the method identifies the set of input values required to invoke the environmental response for the percentile and standard under consideration. It has been tested successfully in a freshwater and a marine example. The method has general applicability in the sense that it is not restricted to a specific model type or environmental system. Uncertainty in applying the method is quantified.