We assessed the potential impact of using coal fly ash to stabilise roadway pavements on groundwater quality and human health. The leaching potential of naturally occurring radionuclides (NORs) typically present in the fly ash was assessed with the HYDRUS-1D code and data representative of a segment of the Wisconsin State Trunk Highway 60 as a case study. Our assessment suggests that the impact would be mainly from the chemical toxicity of uranium (U). In our particular case study, U concentration in the leachate exceeded the maximum contaminant level for this element (MCL = 30 μg L-1) in almost all the scenarios. In the groundwater, the MCL was only exceeded under conditions of high leaching and low dilution in the aquifer. The radiological toxicity from the consumption of the contaminated groundwater by a hypothetical adult, however, was at maximum 43% of the individual dose criterion (IDC = 0.1 mSv y-1). The results also highlight the need to consider site-specific conditions such as climate and hydrogeology when assessing the environmental impacts of utilizing fly ash in roadway construction applications since they could have profound effects on the assessment findings. There is also a pressing need for reliable and representative data to support realistic assessments.