In situ capping (ISC) of subaqueous waste is a non-removal remediation technique for contaminated sediment that involves leaving sediments in place and isolating them from the environment with a layer of soil and/or sediment material. In situ capping is a viable and efficient remediation technology when applied in areas with appropriate environmental conditions. One of the primary concerns associated with the capping methodology is the stability of the cap layer, and this is considered carefully at the design stage to ensure the cap material provides an adequate level of protection against flow events. The long-term ability of the cap to perform depends on its ability to withstand external hydraulic forces, in particular forces associated with extreme events.
Sediment tracking specialists Partrac Ltd have been working with scientists and engineers at the USA Engineer Research and Development Center (ERDC) Environmental Laboratory (Vicksburg, MS, USA) to apply the sediment tracking methodology to underpin evaluations of cap stability. This approach involves strategic placement of uniquely identifiable fluorescent-magnetic sediments (tracers) within the cap layer to directly assess the stability or erosion of cap materials. Tracer particles have been fabricated with properties similar to placed cap materials. Careful, georeferenced placement of batches of tracer of differing colours will be undertaken by ERDC staff and recurrent sampling through time will indicate directly net erosion or net deposition across the site. The technique provides a relatively simple and immediate visual means with which to assess cap stability, and since it is a field technique it reflects real world processes and documents natural episodes of sediment transport.
Partrac designed the fluorescent-magnetic tracer which was hydraulically matched to the cap material in terms of size distribution, density and sphericity. Partrac also provided a detailed Quality Assurance Project Plan (QAPP) to inform the long-term monitoring program. Monitoring of the Partrac tracer material will inform evaluations of the overall effectiveness of the cap design and serve as a key indicator in the site’s cap performance monitoring plan.
For more information on geological tracer and guidance on the sediment tracking methodology contact Dr Matt Wright 00 44 191 242 1302 firstname.lastname@example.org