Transport and geochemical processes controlling the chemical and isotopic composition of pore waters in the upper 45 m of a thick, surficial, clay‐rich till (Battleford Formation) were studied. The upper 3 m of the till is oxidized and fractured. The remaining 77 m of the till (the aquitard) is nonfractured and unoxidized. Concentrations of total dissolved solids, SO₄²⁻, Na⁺, Mg²⁺, and K⁺ decrease with depth through the unoxidized zone to a depth of about 15 m below ground, below which the concentrations remain constant. A similar trend was observed for alkalinity; however, the decrease in concentration occurs over 20 m. In contrast to these ions, Ca²⁺ concentrations increase with depth through the upper 20‐m unoxidized zone, below which the concentrations remain relatively constant. The distribution of dissolved ions shows the presence of two end‐members: elevated solute concentrations in the oxidized zone attributed to geochemical weathering that occurred since the start of the Holocene and connate Pleistocene‐age water at depths between 20 and 45 m. Abiotic and biotic geochemical reaction rates in the aquitard were shown to be extremely slow or not occurring.