International Dredging Review

International Dredging Review

Schematic drawing of the dredging sites at Esbjerg harbor: The red areas have the most contaminated sediment which have to go to RGS90 a licensed recycling company for treatment. The yellow areas are very slightly contaminated and are allowed by law to be placed in the North Sea in accordance with the permit for disposal of dredged sediment.

In late November 2014 the Danish Ministry of Environment Esbjerg Municipality and the Port Authority of Esbjerg announced an agreement on a long-term comprehensive plan for cleaning up contaminated sediment in the harbor of Esbjerg. Plans for the removal of contaminated sediment started in late 2015 and the dredging began in mid-July 2016. It should be completed in May 2019 if not sooner. Other work will continue through 2025 at which time the harbor should be completely cleaned. 

The Danish Coastal Authority awarded the contract to the Danish dredging company Rohde Nielsen A/S which is executing the cleanup with various equipment including two self-propelled barges Hugin R and Munin R and the dredge Toste R. The Toste R is fitted with a special CableArm 3.5-cubic-meter (4.6-cubic-yard) environmental clamshell capable of grabbing the sediment with in-situ water content. 

The agreement between the port and the Danish Coastal Authority includes the purification of contaminated material from the harbor for the next 10 years after which the port should be thoroughly cleaned. The solution will cost the Danish government some 260 million kroner ($36 mil-lion USD). The first 65 million kroner ($ 9.5 million USD) were allocated in the 2015 budget and the remainder in the budget for 2016.  

The dredging part of the contract is valued at some $10 million USD and encompasses the removal of 440000 cubic meters (almost 575500 cubic yards) of contaminated sediment from the port’s basins. Of that mate-rial some 250000 cubic meters (326987 cubic yards) of less contaminated sediment will be placed at designated areas in the North Sea located about 27 kilometers (17 miles) from the port. The other 190000 cubic meters (248510 cubic yards) of highly contaminated sediment mostly with TBT will be are required to be transferred to an RGS 90 licensed landfill site. RGS 90 A /S (Mining and Recycling Company of 1990) is a recycling company with 22 reception facilities in Denmark. The scope of cleanup work at the port includes Basins 1 2 5 and 6 the area located immediately in front of the slipway and the slipway in basin No. 5. 

As stipulated by the Danish Coastal Authority all cleaning is being performed with an environmental dredge equipped with “a grab without teeth.” The CableArm clamshell fits this description as it has strong rubber seals which prevent material from being spilled. During cleaning the vessel must log its position and the function of the depth clamshell at all times and all documentation must be recorded electronically.

A large electric powered air compressor station is installed to feed a double bubble screen which crosses the entrance to the basin thus pre-venting the spread of the sediment during the dredging operations. The contaminated sediment is then lifted from the barges by a hydraulic clam-shell crane and placed into tight container trucks. The sediment is trans-ported 3.5 kilometers (a little more than two miles) to a licensed land deposit for treatment where it is unloaded in available flat basins. The process also requires that the trucks be fully cleaned before returning to the port. The sediment is levelled by bulldozers in 40-centimeter (almost 16-inch) layers and treated with cement to stabilize the contamination. When this process is completed the sediment is ready for final placement and reuse in for instance noise protection bunds. In this way the sand is being disposed of in an environmentally safe manner: Much of it is being recycled and the rest is being deposited in a permitted landfill.

The Port of Esbjerg is an important economic hub for Denmark. It is Denmark’s largest port on the North Sea facing westward toward the rich oil and gas fields of Northern Europe. For that reason Esbjerg is the pri-mary service and supply port for Denmark’s oil and gas industry as well as a Northern European hub for cargo especially RoRo-transport such as wheeled cargo which is driven on and off vessels. The Port of Esbjerg is also the European market leader for handling and shipping out wind power. More than 80 percent of the offshore wind capacity installed in Europe has been shipped out from Esbjerg. On any given day the port can be seen crowded with multiple oil and gas jack-up installation vessels and drilling rigs returning to port for maintenance and service while others are in port awaiting new assignments. 

Esbjerg is also home to more than 200 companies which together em-ploy more than 8000 people. These companies are crucial to the entire supply chain within the European offshore and energy industries.

The Danish Coastal Authority (Kystdirektoratet) is the official coastal government agency authorizing the cleanup operation. It is a division of The Danish Ministry of the Environment but is an independent authority responsible for Denmark’s 7300 kilometer long coastline and for managing the government’s socio-economic interests within the field of coastal protection.