Fracture permeability and groundwater flow in clayey till near Saskatoon, Saskatchewan

Abstract

Field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude. Such findings are common for weathered till but are rare for unweathered till, and have important implications for groundwater recharge and contaminant transport. The till in question is 6 m thick and appears to be unweathered and unfractured. It is overlain by 12 m of weathered and highly fractured till. Results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3.5 × 10−11 m∙s−1 and a mean specific storage of 1.3 × 10−4 m−1. Results of slug tests yield a horizontal hydraulic conductivity of about 5 × 10−9 m∙s−1. Drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4.5 × 10−5m2∙s−1. The slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 × 10−5 m2∙s−1. Geochemical patterns, tritium data, and measured seepage fluxes from an ephemeral pond also indicate that the vertical conductivity of the unweathered till is much higher than the value obtained from the consolidation tests. The data thus show that the unweathered till has significant vertical and horizontal fracture permeability. Key words: till, permeability, fracture, groundwater recharge, contaminant transport.