Chandler Noyes, Jennifer C McIntosh , Nicholas Dutka, Rebecca Tyne, Matthew Lindsay, Grant Ferguson

Continental glaciations during the Pleistocene Epoch created complex systems of aquifers and aquitards across many northern regions of the Earth. The low hydraulic conductivities of glacial till aquitards suggest that limited recharge will reach the underlying aquifers, potentially preserving old groundwaters. Here, we characterize the recharge history in intertill and buried valley aquifers in Saskatchewan, Canada using ¹⁴C, ³H, ⁴He δ²H, δ¹⁸O and major ions. Intertill aquifers with depths of <30 m had corrected ¹⁴C ages ranging from 0 to 15.5 ka. These aquifers also contained ³H and/or elevated NO₃ in some locations, indicating that a component of modern recharge had mixed with older water. A single sample from the Judith River bedrock aquifer in the region had a corrected ¹⁴C age of 10.2 ka and elevated NO₃. Samples from buried valley aquifers with depths of 89 to 123 m contained older waters with ages >38 ka in some locations, indicating that recharge occurred before the last glacial advance over the region . While measuring tracers that cover a wide range of ages is necessary to understand these flow systems, δ²H and δ¹⁸O were less diagnostic because values of modern winter precipitation overlapped with groundwaters with a wide range of ages. The range of ages present in the intertill aquifers of the region indicate that these systems are currently being recharged, which indicates some development of groundwater resources is possible but also points to a need for groundwater protection measures.