Sediment Fabric and Anisotropy of Hydraulic Conductivity in Sandy Till, Wisconsin, U.S.A.

The orientation of macroscopic and microscopic particles in silty, sandy basal till appears to have little effect on aquifer anisotropy. The orientation of 108 elongate pebble and cobble-sized particles was measured in a trench adjacent to 25 wells screened in the till. In addition, the orientation of elongate silt and sand-sized particles was measured in thin sections of five oriented samples taken from the same trench. The orientations of the macro- and microfabric measurements agree with each other and with drumlin orientations in the vicinity. There is no preferential direction of transmissivity (i.e. no horizontal anisotropy) based on analysis of pumping test data. This is most likely due to the relatively small number of elongated, and therefore oriented, particles in the matrix.