Hydraulic conductivity is commonly estimated from grain size characteristics of unconsolidated sediments. We present an extensive set of air-permeability and grain size measurements from a heterogeneous aquifer. These data are unique in that the hydraulic conductivity measurements are made on undisturbed in-situ sediment and, like the grain size measurements, have a small sample volume size (<1200 cm3). Hydraulic conductivity estimated from grain-size has a higher mean and a lower variance than direct measurements. While grain size estimates of hydraulic conductivity do not correspond well to field measured hydraulic conductivity, spatial correlation of the two data sets is quite similar. ¿ 2001 American Geophysical Union