Field and laboratory determination of the hydraulic diffusivity of a confining bed

The field and laboratory evaluations of the hydraulic diffusivity of a confining bed are presented. The field approach consisted of measuring the head in the confining layer by placing piezometers equipped with differential pressure transducers at different depths in the confining layer. Pumping from the overlying aquifer resulted in an observed head change at the aquifer confining bed interface which for long periods of time could be approximated by a step drawdown. The best fit of observed data to the set of theoretical type curves for the step drawdown solution yields a hydraulic diffusivity, K' / S' S , of 2.9 × 10 −2 cm 2 /sec. Hydraulic diffusivity values for the natural effective load, as obtained in the laboratory using consolidation techniques, are in general agreement with this result. Hydraulic conductivity values as determined in the laboratory by consolidation and constant flow methods are generally similar for the same sample. Particle size distribution and the clay mineralogy are also given for each sample.