Evaluating the Impact of Geophysical Variables on the Bacterial Contamination of Private Wells in Southern Ontario

Abstract

Bacterial contamination in groundwater is not often analyzed beyond local and regional scales. The presence of bacterial contaminants in the groundwater of southern Ontario has been observed, and several areas have been identified as being at higher relative risk of E. coli contamination (Krolik et al, 2013). This discovery by Public Health Ontario has prompted further research to evaluate relationships between observed levels of bacterial contamination and the geological setting of private wells. Using approximately 38,000 geocoded wells, statistical analysis was performed to compare overburden depth, soil texture, bedrock classification, and surficial deposit classification to observed levels of total coliform bacteria and E. coli. A very weak negative correlation was observed between overburden depth and E. coli, but not total coliform bacteria. One-Way ANOVA identified statistically significant differences among the means of total coliform bacteria counts in bedrock and surficial units, but not for E. coli. One-Way ANOVA identified statistically significant differences among the means of both total coliform bacteria and E. coli in wells situated in soils of different texture.