Environmental dredging of a chromium-contaminated fjord in Valdemarsvik, Sweden
Type:
Presented during:
CEDA Dredging Days 2015 - Innovative Dredging Solutions for Ports, Rotterdam
Authors:
Pensaert S, Nollet H, Rombaut E and Lepère X - DEME Environmental Contractors, Belgium
Abstract: The sediments in Valdemarsviken have been contaminated with chromium from earlier discharge of untreated wastewater from tannery operations. The remediation of the Valdemarsvik fjord is very important for the water quality in the Baltic Sea. Contaminated sediments in the inner part of Valdemarsviken were dredged, dewatered, stabilized and placed as fill on land. As dredging of the sediments in these areas would affect the stability conditions along parts of the shores and therefore required the stabilization of quays, shores and the landfill area by lime-cement columns. The dredging of contaminated sediments covered about 200,000 m³ spread over a 350,000 m² large area. During a detailed design phase, prior to the start of the works, the site conditions and sediments were monitored and investigated thoroughly. Lab scale tests were performed to verify that the chosen process for the dredging, dewatering and stabilization meet the set requirements as regards to strength of the backfilled stabilized sediments specified by the client. The lab work also formed the basis of process design for the on-site solidification plant. The dredging operations met the stringent environmental demands towards turbidity and the generation of spill. The sediments were dredged by using a hydraulic excavators equipped with a level-cut clamshell bucket or a visor bucket. The dredged sediments were pumped to a continuous mixing unit where they were stabilized with a cementitious binder. Any water released from the activities was collected and treated by a specially designed on-site water treatment plant.
Keywords: environmental dredging, soil reinforcement, solidification, stabilization of sediments, level-cut clamshell