Human health risk-based design of ocean outfalls

In recent years there has been a trend towards specifying water quality guidelines from an epidemiological view-point. This raises the possibility that ocean outfall design could itself be looked at from the point of view of the risk to human health from exposure to specific pollutants. An approach to health risk-based design of ocean outfalls is presented in this paper. The approach is based on an integration of the principles of human health risk assessment and ocean outfall design. Hazard identification of rotavirus-used as an example of a typical pathogen in sewage-and dose-response relationships are reviewed. An empirical initial dilution model is combined with secondary dilution and decay models to quantify virus exposures during swimming. The health risk to a swimmer at a specified distance from the outfall discharge is then evaluated by integrating the exposure and dose-response models. Risk of infection, clinical illness, and mortality are all evaluated with a case study using data from an existing outfall. The applicability of the approach to ocean outfall design is presented by quantifying the risks of using a public beach for swimming for a given outfall design scenario. Different scenarios are used to simulate the risk of infection, clinical illness, and mortality, from which the location of the designed outfall may be determined to better assure the safety of swimming areas. A probabilistic analysis is presented to investigate the uncertainty in estimated health risk from potential design scenarios.