The hydraulic diffusivity of a confining bed exhibiting vertical heterogeneity was determined by field and laboratory tests. A thin sand aquifer was pumped, and head changes were observed in the aquifer and at three vertically separated piezometers in the overlying confining bed. A four‐layer digital model was used to analyze the field data. Hydraulic diffusivities for each layer were adjusted in the model until calculated head changes in all piezometers closely matched those observed in the field. Laboratory‐determined hydraulic diffusivities were several orders of magnitude smaller than the field‐determined values. Interfingering of layers within the confining bed is believed to have caused this difference. Additional studies are needed before a general conclusion can be reached on the value of laboratory determinations of hydraulic parameters for heterogeneous confining
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