Water exposure and health impacts of recreational waters in an urban watershed

Abstract

As currently implemented, the Clean Water Act’s (CWA) goals that waters be “fishable and swimmable” have been translated to general water quality criteria set based upon the use designation of a particular waterbody. Though those criteria are generally protective of the nation’s waters, they do not always reflect the specific risk of illness posed by recreational use of a particular waterbody. The object of this work is to quantify the risk of excess morbidity associated with recreational use of three urban waterbodies. Combined Sewer Overflows (CSOs) are found along all of these waterbodies. Using risk assessment, the risk associated with recreation in these waterbodies will be examined for both wet and dry weather conditions.Risk assessment is a method by which the health hazard associated with contact with a certain substance or participation in a particular activity can be measured. Using this method, risk is calculated as the probability of contact or participation occurring multiplied by the severity of the harm brought on by the contact or participation.Quantitative risk estimates were developed for Enterococcus spp. and E. coli at each of 7 sites where water sampling was conducted. Individual as well as overall daily risk estimates for excess morbidity were based on measured concentrations of bacterial indicator organisms and observed use patterns at sites on the waters where use was most frequent. The Crystal Ball statistical package for Microsoft Excel was used to estimate the risk by Monte Carlo analysis, where the inputs were distributions of bacterial concentrations and use frequency which were fitted individually for each site where data was collected, as well as appropriate dose-response functions.In theory, if a CSO discharge results in an increase in indicator bacteria concentration in a body of water and therefore an increase in the risk of illness due to contact with that water, it is expected that there would be a larger difference in risk due to contact with water upstream when compared with water downstream of the CSO when it is discharging (wet weather) than when it is not discharging (dry weather).As an increase in risk was not seen, CSO discharge doesn’t appear to influence water quality and the associated risk from water recreation. At both sites on Waterbody 1 where samples were taken both upstream and downstream of CSOs, there was no change in the difference in risk due to contact with water upstream when compared with water downstream of the CSO during wet weather as compared to dry weather. On Waterbody 3, there appeared to be some change in the difference in risk between the two sites, but that change was almost eliminated when the estimated ingested dose of recreators was taken into account.The minimal effect of CSO discharge on indicator organism concentration indicates that any organisms present in the waters that were sampled were likely carried from upstream locations. This also indicates that any remedial strategies that focus exclusively on CSOs, such as outflow holding tanks…