Microbial risk assessment for recreational use of the Kranji Reservoir, Singapore
Author(s)Dixon, Cameron Chaffee
Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.
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The Public Utilities Board of Singapore is responsible for management of the Kranji drinking water reservoir and wishes to open the reservoir for recreational water use as part of their "Active, Beautiful, and Clean Waters Programme". A field campaign was conducted at the Kranji Reservoir to determine the microbial water and sediment quality of the reservoir for use in a model that predicts the risk of gastrointestinal illness due to recreational use of the reservoir. Water samples were collected at seven locations throughout the reservoir and sediment samples were collected at two locations located near the shore. The samples were then analyzed for Enterococci concentrations using a most probable number method. The measured geometric mean concentrations found during the field campaign were 13.3 Enterococci colony forming units (CFU) per 100 ml water and 1400 Enterococci CFU per gram sediment. Based on the strengths and weaknesses of available statistics-based risk models, a model by Wiedenmann was chosen based on the flexibility of the model and the quality of the underlying epidemiological study. Using the model, no-observed-adverse-effect-level guideline concentrations of 25 Enterococci CFU per 100 ml for swimming, 51 Enterococci CFU per 100 ml for kayaking and 860 Enterococci CFU per gram sediment for wading were calculated. Based on all available bacterial measurements of the Kranji Reservoir, an interim geometric mean guideline of 25 Enterococci CFU per 100 ml water and 860 Enterococci CFU per gram sediment is suggested.(cont.) Single-sample maximums for a monitoring program should be set to 96 Enterococci CFU per 100 ml water and 2,500 Enterococci CFU per gram sediment. These guidelines should be applied to the area of the reservoir open to recreation, which should be restricted to the northern main section of the reservoir. Entry and exit from the reservoir and wading should be restricted to a smaller area of shoreline until more sediment samples are taken to determine safe entry and exit areas. Final geometric mean and single-sample maximum guidelines should be based on a study of the pathogen-to-indicator-bacteria ratios in the Kranji Reservoir.
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaves 69-72).
DepartmentMassachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.
Massachusetts Institute of Technology
Civil and Environmental Engineering.