Geochemistry of Selected Glacial and Bedrock Geologic Units, Cold Lake Area, Alberta

Alberta Environmental Protection (AEP) initiated this study on a request for background information to explain elevated arsenic levels in groundwater from glacial aquifers in the Cold Lake area. One of the questions raised was if naturally occurring arsenic levels in the glacial sediments could be contributing arsenic to the groundwater. This report presents the results of two geochemical analysis procedures performed on glacial till, clay, and bedrock samples collected by the Alberta Geological Survey (AGS) more than 20 years ago. Archival samples of till, clay, sand and bedrock claystone from a select number of auger testhole sites in the Cold Lake area were retrieved and more than 175 samples were prepared for geochemical analysis. The results show that for some elements, there are strong contrasting chemical signatures between the glacial sediments and the underlying claystone of the Colorado Group. Arsenic is present in both glacial and bedrock materials, and its values appears to show one of the strongest contrasts between glacial till and bedrock claystone. Differences in chemical signature can be observed between some of the till units, though they are not well defined. No comments are made as to the relationship between chemical composition of the sediment and the composition of the groundwater.