Investigation of Private Well Water Quality in Southeastern Ontario Using Geographic Information Systems and Molecular Microbial Source Tracking Tools

Abstract

In Canada, as in many other affluent nations, private well water consumers remain at risk for gastrointestinal (GI) illness due to fecal contamination of groundwater. There have been numerous documented outbreaks of GI illness related to contaminated drinking water. While the general risk to well water consumers has been established, the risk in southern Ontario is poorly understood. As a preliminary step towards understanding this risk, a study of Escherichia coli (E. coli) contamination in private well water was undertaken. Spatial scan statistics were employed to determine the extent of contamination for over 30,000 private wells in southeastern Ontario between 2008 and 2012, inclusive. This analysis revealed one large, temporally stable elevated risk region, and three significant smaller regions within it. The methodology utilized in the primary investigation was then applied to a 2012 dataset for all of southern Ontario, resulting in the identification of three regions of elevated risk. The presence of E. coli, a traditional fecal indicator organism, indicates lack of water potability. To provide knowledge regarding the origins of fecal contamination in southeastern Ontario, a molecular microbial source tracking (MST) study was undertaken. A quantitative real-time Bacteroidales PCR assay specifically targeting human, bovine, and general (specific to 10 hosts) was optimized and applied to 716 private well water samples. Almost half of the samples showed evidence of human fecal contamination, whereas only 13% contained evidence of bovine fecal contamination. Approximately one quarter of well samples tested positive for the general host Bacteroidales assay, with an additional one quarter testing negative for all MST assays. Additionally, spatial scan statistics revealed a region of human-sourced contamination, which geographically corresponded with the E. coli contamination cluster for the same study year. The presence of E. coli contamination clusters among private wells reveals an at-risk group of well water consumers. As such, public health practitioners may use this information to target well stewardship programs in higher risk regions. Humans were the predominant contributors of fecal contamination to private wells within the primary study region. These findings may enable future preventative measures by providing insight into the true origins of groundwater fecal pollution.