The Use of Radionuclides to Identify Vulnerable Fractured and Karst Bedrock Aquifers in Eastern Ontario

Abstract

Domestic water wells in Eastern Ontario were identified in potentially vulnerable fractured and karst bedrock aquifers using geologic and geochemical data. A novel methodology is presented that evaluates ¹³⁷Cs and ²¹⁰Pbₑₓ as local indicators of groundwater vulnerability. The method is designed to determine the vulnerability of a specific well. Suspended sediment samples and well-bottom sediment samples were collected from both potentially vulnerable and non-vulnerable wells. Surface soil samples were also collected from West Rural Ottawa and the Township of Alfred & Plantagenet in Ontario, Canada. Gamma spectroscopy was used to analyze the samples and quantify the presence of the radionuclides in cps and cps/g. The spectral data indicate no significant difference in the activities of ²¹⁰Pbₑₓ among samples, but a significant difference in the activities of ¹³⁷Cs was observed between surface soil samples and well-bottom sediment samples collected from vulnerable wells. The data suggest that ²¹⁰Pbₑₓ does not act as a good indicator of vulnerable aquifers because of its geogenic origin. The anthropogenic origin of ¹³⁷Cs precludes this issue, and while ¹³⁷Cs was detected in measurable quantities at the surface, its use as an indicator of vulnerable aquifers is limited by hydrologic and geologic controls that prevent infiltration in vulnerable terrains.