Annual report 2019

67

COMPLEXITY LNGC is being built at a location where industrial activities in the past have polluted the bed of the port. “A large part of our work consists of removing and cleaning up all kinds of soil,” Dekker explained. “In both sections of the port different environmental requirements apply. An extensive environmental monitoring program has been set up with measuring buoys and water- and soil sampling. We can’t process all the polluted material in the same way and that makes this work very complex. Our colleagues from Hydronamic and Boskalis Environmental have developed a specifc approach for each type of contaminated soil. There are two types of contaminated soil in each area: Industrial Landfll plus (IL+) and Industrial Landfll minus (IL-).” PROCESSING “The cleaning processes for contaminated soil are extremely labor-intensive,” Dekker said. “Barges are unloaded at the quay wall and any water released is pumped through the water treatment plant. Dump trucks take the material to the landfll. The IL+ material from the area where the aluminum company was based is stored on shore in a pre-prepared landfll, where colleagues from Cofra came in to help us apply a watertight liner. Once the landfll is full, the top is also covered with a liner after which the whole disposal site is being covered with a capping layer of soil. The dredged IL+ material from the LNGC area is unloaded at the quay wall, dewatered and temporarily stored in twelve pre-prepared bunkers with a capacity of 300 cubic meters each. After the material has been tested for its dry solids content, it is moved to one of the three warehouses. As required by the client, the material is then mixed with cement to stabilize it before it is transported in barges to another port for onward land transport and disposal. The barges with IL- material from the site of the ore and aluminum company are unloaded at the quay wall. The material is then dewatered and taken by dump trucks to a pre-prepared landfll. The barges with LNGC IL- material are maneuvered alongside the specially prepared mobile barge unloading dredger. That dredger has been ftted out with four excavators, two with a grab to remove debris and two with a pump and water jet to pump the material from the barges through a pipeline to the pre-prepared LNGC IL- landfll. Both IL- landflls will also have to be covered by a soil capping layer after they have been flled.”

PREVENTING SPILLAGE Dekker described all the measures, procedures and inspections relating to safe working and preventing environmental damage during the work. “The trucks that take contaminated soil to the landflls are carefully monitored,” is one example he gave. “We do everything we can to prevent spillages. Every possible infringement is recorded. So the trucks are not fully loaded and we have had steel plates welded at the location of the tailgate of the dump trucks to prevent leakages of water or material. We have installed plastic screens and containment barriers on the route to the landflls to stop contaminated soil entering the open water. Should there be a spillage, a report is made and our environmental monitoring crews clear it up immediately. They check the route of the trucks by car. And, in turn, they are monitored by inspectors appointed by the client. In this way, almost every aspect of our work is carefully inspected on a daily basis, both by ourselves and by the client, and this is done in good mutual consultation.” DEPOSITING CLEAN DREDGED MATERIAL In addition, the cutter suction dredger Edax dredged more than a million cubic meters of clean soil. “That material was taken to an offshore site and deposited using an indirect approach,” Dekker said. “To prevent turbidity, the Edax frst pumped the dredged material through a floating pipeline to the trailing suction hopper dredgers Beachway and Shoreway. They then took it to the designated disposal location about three kilometers from the project site where they lowered the suction pipe to twenty meters below the surface and deposited the material from the hopper by pumping it back through the suction pipe. This method was also developed to meet the strict environmental permit requirements.” ROAD TO COMPLETION One more season remains for Boskalis to complete the works which will be undertaken in the period from September 2020 until February 2021. Although the majority of the dredging is done a quantity remains to be removed which could not be dredged in the second season as a buffer was required to be maintained in place in front of the future quay walls to ensure their stability during construction. Following completion of these quay walls Boskalis can resume the dredging and remove this outstanding volume.