Hydraulic conductivities of a portion of the Twin Lake aquifer are derived from grain size analyses performed at 3-cm vertical sampling intervals in four boreholes, spaced 1 m apart. Correlation of conductivity logs between four boreholes leads to a geometrical model which corresponds closely to the spatial structure derived from the velocity field of previous tracer tests. Histogram and correlogram analyses of conductivities agree closely with those of velocities, and the two data sets appear equally useful for characterizing the aquifer and its spatial variability. Using Darcy's law, flow velocities and conductivities are combined to calculate a theoretical, hydraulic gradient. Comparison to gradients observed at the site reveals agreement on a large scale. however, differences exist in detail because observed piezometric heads fail to reflect small-scale heterogeneity. Since these differences are significant for contaminant transport prediction, it is recommended for further studies to directly measure flow velocities from a tracer experiment, rather than to reply on head measurements and on Darcy's law for the calculation of transport parameters. ¿ American Geophysical Union 1993