Describes the results of a detailed investigation program of the black soils of the Liverpool Plains, New South Wales, to determine the origin of high bulk electrical conductivity anomalies measured using a GEONICS EM31. Minimally disturbed core was obtained to 10m depth at four locations. Core was split into 100mm increments and tested for moisture content, cation exchange capacity, laboratory conductivity, grain size, XRD and fluid chemistry of 1:5 extracts. Field investigations involved conductivity imaging and borehole logging. The results show that the soils are a uniform smectite clay to 10m depth with the EM31 response caused by differing salinity waters held within the clay by surface tension.