Disinfection Vs Non-Disinfection Microbial Risk Assessment For Recreational Use Of Chicago Area Waterways

This study was conducted to estimate the human health risks from recreational use of the Chicago Waterway System (CWS) receiving treated, but non-disinfected, effluent from the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC or District) North Side, Stickney and Calumet water reclamation plants (WRPs). Dry and wet weather samples were collected within the recreational season and analyzed for indicator and pathogen bacteria, protozoa and viruses. The dry and wet weather microbial results were integrated in a probabilistic microbial risk assessment (MRA). Recreational activities considered were canoeing, boating and fishing. Exposure parameters were developed from the primary literature and local use surveys. Overall rates of illness for receptors were all below the USEPA limit of 14 illnesses per 1000 exposure events for freshwater recreational use. Higher rates of illness were predicted during wet weather events. Disinfection of WRP effluent alone has marginal effects on overall recreational illness rates.