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Covering Solutions Executive Summary - Topic Area 5.1 Environmental Resources Management with AMBIOS Environmental Consultants Ltd and Waterways Experimental Station This study is part of the UKOOA Joint Industry Research Programme and is concerned with the practicality of covering cuttings piles in situ. Two main methods of disposal and containment of wastes in the marine environment have been identified; in situ capping in which the contaminated material is left in place and is covered with a capping layer, and Confined Aquatic Disposal (CAD) in which the contaminated material is moved to an excavated pit and then capped. The only example of in situ capping identified is from Japan. CAD has been adopted in a number of countries, principally the USA and Hong Kong and has been demonstrated to achieve containment of the deposited material. The techniques examined in this report are therefore proven to be technically feasible in at least some situations. The study team developed a total of nine outline designs for CAD and in situ capping which included different options for both chemical confinement and physical protection ie rock armour or concrete mattresses. These were screened using high level design criteria. All of the potential designs satisfied these criteria and were therefore considered in more detail. In general, CAD designs were anticipated to be less feasible, cause a greater environmental effect and be more expensive than in situ capping. The use of a CAD site requires the removal of cuttings material and placement in the containment pit during which significant release of cuttings material may occur. CAD is significantly more expensive than in situ capping but there are economies of scale for both options. In engineering terms capping in situ with an armour stone/gravel layer over an absorbent sand layer was considered to be the most feasible option. Chemical isolation of the confined material would be achieved by providing an absorbent layer of sand into which contaminated pore water, expelled during the settling (consolidation) of the deposited material, will be retained. The use of membranes was considered to be unfeasible and was not considered further. Biological isolation will be achieved by use of a thick cap of coarse sediment. Physical isolation is provided by the top armour layer. In comparison with the placement of armour stone, it is considered that the mattress cap would be costly, time consuming and less safe to construct. It would also be more prone to damage by anchoring and trawling. Robustness of the armour stone design can be provided through the use of appropriate materials, but ongoing monitoring would nevertheless be required. Because of the depth of the Central and Northern North Sea it is estimated that the cap design using rock armour over gravel and sand would be sufficient to resist erosion by storm waves. The armour stone cap would be hazardous to fishing vessels. However it is likely to be unacceptable to prohibit fishing in the area of the disposal site. By covering the armour with an additional layer of gravel it may be possible to create a trawlable surface without compromising performance of the cap. Escape of contaminants from CAD sites in Hong Kong through diffusion is not considered to be significant. Stakeholder concerns and conflicts may be complex and difficult to resolve.