Pathogens

Tracking the fate of pathogens and identifying the source of pathogens is critical for developing engineering alternatives to reduce the risk of contracting waterborne diseases in recreational waters and reduce contamination in shellfish areas. The detection and enumeration of all pathogens is usually impractical due to a lack of readily available and affordable methods for testing. Therefore, the use of indicator organisms has provided regulators with a means to ascertain the likelihood that human pathogens may be present in recreational and shellfish waters. The most widely used indicators have been total coliform and fecal coliform bacteria. However, following epidemiological studies, EPA has promulgated the use of E.coli for fresh recreational waters and Enterococcus for both fresh and marine recreational waters.

HydroQual has modeled pathogen indicators for over 25 years in both fresh water and marine environments. In general, the sources of pathogens to the receiving water are episodic since the discharges are primarily driven by rainfall events. Therefore, the models used to characterize the sources and fate of pathogens must be able to simulate the time-varying nature of pathogen loadings and receiving water responses.

HydroQual uses three modeling frameworks to track the fate of pathogen indicators:

1. A rainfall/runoff model to characterize the flows and loadings to the receiving waters
   
   
2. A hydrodynamic model to calculate dilution and receiving water movement, and
   
   
3. A water quality model to track the fate of pathogen indicators (e.g., total and fecal coliform bacteria and/or enterococci). The water quality model uses a decay coefficient of the indicator bacteria; which is usually a function of temperature, salinity (marine environments), and solar radiation. This modeling framework has been applied to water-bodies world-wide.

HydroQual has also developed desktop tools that may be used by regional and local Departments of Health to assist in the determination of when it is necessary to close public bathing beaches and/or issue wet weather advisories.