A novel method for sampling and characterizing unconsolidated deep vadose zones

This technical note describes a novel large diameter vadose zone sampler (VZS) that has been developed to permit easy and safe access to deep unconsolidated vadose zone profiles and the gathering of information that has not been possible previously. The purpose is to allow investigations to be performed cost effectively at locations of interest rather than being restricted to areas with suitable exposures. The VZS is designed to be used with 1.2-m-diameter auger holes and consists of a light-weight crane and several 1.15-m-diameter, 1.5-m-high, cylindrical steel sections, which bolt together to provide a temporary casing for the auger hole. The sections have removable openings to permit examination and sampling of the vadose zone profile. The VZS is relatively inexpensive to construct and has been designed to be mobile and provide access to the vadose zone at a wide range of locations, rather than the usual restriction to available outcrops in cuttings or gravel pits. We describe the use of the VZS to characterize the profile of an alluvial gravel system at four locations in Canterbury, New Zealand and to carry out a field calibration for a neutron probe that had been installed to a depth of 3 m into an alluvial gravel profile. The VZS enabled collection of samples for physical, chemical, and gravimetric moisture determination at precise depth locations. This information will ultimately lead to better characterization and understanding of water and contaminant transport and transformation through vadose zones.