Characterising sediment physical property variability for bench-scale dewatering purposes

A field sampling programme was undertaken to assess the variability of physical characteristics of contaminated sediments in a large (160 ha) effluent stabilisation lagoon. The objective of this paper is to use this 'field lab' as a basis for comparing different sampling techniques (i.e. discrete and composite) for remediation-based evaluations (i.e. sediment volume estimates and bench-scale dewatering studies). The distribution of sediment thickness measured throughout the lagoon by gravity core sampling is presented for context. Selected gravity core sediment samples are evaluated with respect to physical property (water/solids content, bulk density and particle size) variability in both the vertical (i.e. within a single gravity core) and spatial directions (among gravity cores). Composite samples are created by way of homogenisation of a single entire gravity core to compare their properties to the discrete and average physical properties of a nearby gravity core. Vacuum-based samples are also compared to gravity core samples in terms of particle size. It is demonstrated that by understanding sediment variability, composite samples can be shown to be an efficient method of obtaining representative samples. When large samples for dewatering trials are required, vacuum sampling can produce samples with similar mean particle size to discrete and composite samples.