The State of California's WastewaterReclamationCriteria is under review and will be revised and expanded to include several new regulations on the use of reclaimed municipal wastewater. To provide a scientific basis for the evaluation of the existing and proposed Criteria, enteric virus monitoring data from secondary and tertiary effluents were evaluated. These virus data were obtained from special studies and monitoring reports, covering the period from 1975 to 1989, including ten municipal wastewater treatment facilities in California. Based on the enteric virus data from these reports, and using the current Criteria as a guide, four exposure scenarios were developed to determine the risk of waterborne enteric virus infection to humans as a consequence of wastewater reclamation and reuse. The exposure assessments included food crop irrigation, landscape irrigation for golf courses, recreational impoundments, and ground water recharge. The virus enumeration and the resulting risk assessments described in this paper provide a comparative basis for addressing the treatment and fate of enteric viruses in wastewater reclamation and reuse. The analyses show that annual risk of infection from exposure to chlorinated tertiary effluent containing 1 viral unit/100 L in recreational activities such as swimming or golfing is in the range of 10−2 to 10−7, while exposures resulting from food-crop irrigation or groundwater recharge with reclaimed municipal wastewater is in the range of 10−6 to 10−11. The risk analyses are also used to demonstrate that the probability of infection can be further mitigated by controlling exposure to reclaimed wastewater in the use area.

A review of the fate on enteric viruses and phages through each major unit process used in wastewater and potable water treatment is given. Starting out with raw sewage, optimized conventional tertiary wastewater treatment with one hour contact and free chlorine residuals can be expected to remove 5-7 logs of viruses leaving <1 infectious unit/1000 liters. However, because engineered systems are not fail safe, prudent public health engineering, planning and design suggest limited direct exposure to reclaimed wastewater. Dilution, indirect reuse, or additional treatment are the suggested approaches until more research is conducted. Only under the special circumstances should direct reuse be proposed.

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This paper was prepared for presentation at the 1999 SPE International Thermal Operations and Heavy Oil Symposium held in Bakersfield, California,17–19 March 1999.

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