ABSTRACTHydrogeologic and isotopic investigations were conducted on thick profiles of clayey glacial till at three study areas in the Interior Plains Region of southern Alberta, Canada. The till consists of an upper weathered zone (9 to 18 m thick) and a lower nonweathered zone (10 to 30 m thick). The presence of tritiated ground water at depths of up to 5 m below the water table in the weathered zones shows that the upper part of the weathered zone is hydrogeologically active. Interpretation of hydraulic head and hydraulic conductivity data, indicates that vertical seepage velocities in the nonweathered till zones range from 2 to 6 m per 1000 years. Calculated lateral ground‐water velocities in the till zones are only about 9 m per 1000 years, and it is concluded that most of the ground water recharging the weathered till zone is returned to the atmosphere by evapotranspiration. Oxygen‐18 and deuterium analyses of ground‐water samples for the weathered till zones support this concl
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