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Application of Microbial Risk Assessment Techniques to Estimate Risk Due to Exposure to Reclaimed Waters

Project: 04-11
Type: Report
Year Released: 2007

Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board
Total Investment: $171,904.03 (Cash: $124,991.06, In-Kind: $46,912.97)

Principal Investigators: Adam W. Olivieri, Dr. PH, P.E, EOA, Inc., and Edmund Seto, Ph.D., University of California at Berkeley

Background

The potential transmission of infectious diseases by pathogenic agents is the most common concern associated with nonpotable water reuse. While several states have developed standards that include treatment process requirements and microbial and other water quality limits, no existing state regulations are based on risk assessment methodology. This has resulted in widely varying criteria among the states that have developed regulations and has raised issues and concerns (both real and perceived) by regulatory agencies, operating agencies, reclaimed water users, and the public in general related to the scientific basis of water reuse regulations and, hence, the public health protection afforded by existing regulations. Microbial Risk Assessment techniques can be used to better define relative health risks associated with exposure to reclaimed water. Through analysis of differing reclaimed water management scenarios and reuse applications, relative health risks may be compared. Relative health risks, using predictive models, can be compared to inform decisions about water reuse projects.

Goals and Objectives

The project assesses microbial risk to provide insight toward understanding the relative risks to human health associated with nonpotable water reuse applications.

Research Approach

To this end, a risk matrix was developed to facilitate understanding of the relative microbial risks associated with the use of reclaimed water for nonpotable reuse applications under a range of different conditions. The conditions evaluated included the occurrence of five infectious agents of public health concern in reclaimed water, the efficacy in reducing pathogen concentrations of two reclaimed water treatment process trains, and the predicted volume of water ingested via three end-use specific exposure pathways.

Findings and Conclusions

The information presented in this report will be useful to water and wastewater utility managers, regulators, and water quality scientists and engineers because it is based on scientifically defensible data that can be used to compare the potential relative risks associated with nonpotable water reuse applications under a wide range of relevant conditions. The estimated risks reported in this investigation are consistent with, although slightly higher than those reported in other literature.

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