TECHNICAL PAPER
Dewatering and Containment of Heavy-Metal Contaminated Sediments with Geotextile Containers and Polymers. Developing and Validating System Performance and Design
K. Bossy; T. Anderson, C.E.T., AScT, EP; T. Kobilnyk
The processing and refining operations at a former mine site in Eastern Canada resulted in significant environmental impact, leaving behind high concentrations of harmful materials such as arsenic, cobalt, copper, nickel, and low-level radioactive material in soil, sediment, surface, and groundwater. To reclaim the site, a project was undertaken to develop and validate a hydraulic process to remove, contain, and dewater contaminated sediments efficiently and effectively, while reducing the handling of material.
The project design included dredging, geotextile containment and filtration, polymer conditioning, pH adjustment, and filtrate management. Geotextile containers provide a reliable, cost-effective way to collect, dewater, and permanently store contaminated sediment on or near the site. The technology has been successfully used for mine reclamation operations and other environmental remediation projects worldwide. The addition of polymers to the dredged slurry can enhance the retention of heavy metals and other contaminants, while also improving the sediment’s dewaterability. The combination of polymer and filtration provided by the woven geotextile produces low total suspended solids in the effluent and is ideal as a pretreatment step allowing for filtrate to be managed separately according to its characteristics. The filtrate produced by the geotextile containers is often suitable for direct discharge to a receiving body.
The paper discusses each step of project development, including bench-scale testing, on-site pilot testing, and the full-scale concept. Performance data is presented on the sediment removal rate, the attained solids of the material, the retention of heavy metal contaminants in dewatered sediment, and the quality of the filtrate produced by the process. The data collected during this preliminary stage informed the design of a large-scale project to dredge, dewater, and permanently store a significant volume of contaminated sediments from the site, while returning treated effluent that met discharge requirements.
