Hydrogeology of a thick clay till and Cretaceous clay sequence, Saskatchewan, Canada

Clay-rich glacial till and Cretaceous clay are common throughout the Interi or Plains of North America. Quantifying groundwater flow through these aqui tards has implications for solute transport in aquitards and protection of underlying aquifers. Groundwater flow through a two-tiered aquitard system was investigated using laboratory and field methods at a test site in Saska tchewan, Canada. The aquitard system consists of 80 m of uniform, plastic c lay-rich Battleford till (deposited 12-18 ka BP) disconformably overlying 7 7 m of late Cretaceous plastic marine clay (Snakebite Member, deposited 70- 72 Ma BP). The upper 3-4 m of till is oxidized and fractured whereas the re mainder is unoxidized. For the scales investigated, results suggested that hydraulic conductivity, K,is independent of scale for relatively thick till and clay bedrock deposits. Analysis of slug tests in the unoxidized till a nd laboratory tests on cores of unoxidized till yielded geometric mean K va lues of 5.4 x 10(-11) and 2.7 x 10(-11) m/s, respectively. Laboratory K tes ts of clay samples yielded a geometric mean K of 4.3 x 10(-12) m/s. Bulk K of the clay was estimated to be 2.3 x 10(-12) m/s assuming steady-state flo w through the till and clay. The present-day groundwater velocity through t he aquitard system was estimated to be between 0.5 and 0.8 m/10 ka downward based on the measured K values, measured hydraulic gradients, and measured porosities. Results suggested that pore water in much of the till was intr oduced during or shortly after glaciation.