Analysis of wet & dry weather bacterial concentrations within Kranji & Marina Catchments, Singapore

Abstract

The Singaporean government's Public Utilities Board aims to open Kranji and Marina Reservoirs to the public for recreational use. Thus, the water bodies have to be safe from fecal contamination in order to protect the people's health during water-contact activities. Under the Singapore-MIT Alliance for Research and Technology (SMART) program, faculty and students from Nanyang Technological University and MIT have worked together to conduct bacteriological studies at both Kranji and Marina catchments and their reservoirs. Storm water, especially from urban landscapes, contains elevated concentrations of total coliform, . coli, and enterococci bacteria. The goal of this study was to review, classify, and evaluate wet- and dryweather bacteria samples dating back to 2005 with a focus on grab-samples collected by Nshimyimana (2010) in 2009 and samples collected during January 2011 field work at Choa Chu Kang Crescent, Bras Basah, and Verde. These bacteriological samples were collected from high density residential (HDR), low density residential, forested, and commercial areas. Evaluation of the relationship between concentration and flow showed a linear increase in bacteria concentrations with flow in storm water from mixed forested and HDR areas, a pattern that is consistent with nonpoint source runoff, while commercial areas exhibited peak concentrations during low and high, but not intermediate, flows indicating contributions from both nonpoint and point sources. Likely point sources are sanitary sewer leakage due to aging infrastructure in the commercial area. All measured concentrations exceeded Singapore and USEPA's recommended bacterial levels for recreational water. Hence, more wet-weather sampling is recommended in order to collect data on bacterial concentrations so that more robust statistical analyses can be performed in future studies. The elevated bacterial concentrations during wet weather from this study indicate that extra precaution should be taken to manage discharge of storm water into receiving waters before they are made accessible to the public.