THE NATURE OF TILL AND DRUMLINS IN PETERBOROUGH AND THE IMPLICATIONS FOR DEVELOPING A COMMUNITY GROUNDWATER SUPPLY

In the Peterborough area of Ontario, Canada, there is a well-documented and extensive drumlin field. While the origin of the drumlins is widely debated despite many years of study, one aspect remains certain; drumlins and till have significant implications for groundwater movement and public water supply. The late Wisconsin Northern Till, deposited by the Laurentide Ice Sheet, is found in the area of the Peterborough drumlin field, and is considered to be a deformation till up to 65 meters thick. The till overlies proglacial and glaciolacustrine sediments and shows considerable textural and thickness variability within the drumlin field. Coarse-grained interbeds are common within the till and allow it to function as a ‘leaky aquitard’ as opposed to most till units which are considered to be regional aquitards. The presence of significant coarse-grained interbeds within the till produces groundwater flow pathways that are not easy to predict and which can have significant implications for contaminant transport and groundwater supply. A First Nations community located within the Peterborough Drumlin field has been attempting to find a more sustainable groundwater supply in the drumlizined terrain. Currently, homes are supplied by private wells. Options are being considered for improving individual wells or developing a communal water supply. A recent field program involved drilling a fully cored and geophysically logged borehole through till on the flanks of a large drumlin as well as the construction of a well by air rotary. The extracted core consists primarily of sand-rich till with interbeds of sand and gravel. Correlation of data between the two recently drilled wells and lithological and hydrogeological data obtained from local water well records allows analysis of the till stratigraphy within this portion of the drumlin field. This till stratigraphy provides a foundation for understanding local groundwater movement and the potential for public water supply. This preliminary interpretation of the local stratigraphy will guide further field work and provide the basis for improving the supply of drinking water for the community.