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12.2 Sediment constituentsNOTE 1 More than 90% of the sediment from navigation dredging is relativelyuncontaminated, natural, undisturbed sediment, and is considered acceptable for awide range of uses (see Environmental aspects of dredging [3]).Planning with respect to the disposal, dispersion and beneficial use of dredgedsediments should take account of the sediment constituents, not just in terms ofphysical characteristics such as particle size but also in terms of likelycontaminants present, and of meeting the criteria essential for the protection ofthe environment. The testing (characterization) of the materials in questionshould be appropriate for the activities planned and the environments wheredredging is being undertaken and those which will receive the materials.Planning of contaminant testing should take into account the potential need forboth chemical testing and microbial testing.An iterative approach to characterization of materials to be dredged should beassessed in terms of its potential benefits, e.g. the first chemical analyses in aproject may be undertaken on a relatively small number of samples for acomprehensive suite of analytes, with the results of such an investigation beingused to inform more detailed investigations on a smaller list of analytes for allsamples.BRITISH STANDARD BS 6349-5:2016©If materials to be dredged are found to be contaminated to such an extent thattheir use could be unacceptable or have to be restricted then treatment of thesediment should be assessed as an option, to evaluate whether this improves thepotential for the materials to be used and whether this is a viable and practicaloption.Remediation dredging involves the removal of contaminated sediments with thepotential to cause harm, and in such cases the need for specialist controlmeasures (e.g. silt curtains) should be carefully assessed.NOTE 2 Disposal options can broadly be divided into three categories: unconfined;confined disposal (3.10); and confined disposal facilities (3.11). Sometimessemi-confined placement options are also referred to.12.3 Beneficial useWhenever and wherever possible, dredging schemes should seek to adopt abeneficial use strategy for the dredged material. There are often advantages toretaining dredged material within the sediment transport cell from which it wasremoved rather than permanently removing it from the sediment transportsystem, and beneficial use schemes of this type should be assessed for viability.NOTE Examples of beneficial use include:• feeding intertidal areas in an estuary to maintain their volume;• promoting the growth of saltmarsh;• maintenance of longshore and other sediment processes;• beach renourishment;• coastal protection;• use of dredged material as a construction aggregate;• flood defences.12.4 Disposal at seaCOMMENTARY ON 12.4Disposal at sea is a common practice for material arising from both capital work andmaintenance dredging, with the dredged material to be disposed of within aspecified licensed area. Such licensed areas are monitored and managed in the UK.In the UK, as in many other parts of the world, disposal at sea is controlled bylegislation.If beneficial use of dredged materials is not a viable option then disposal shouldbe assessed as an option. Familiarity with the licensing process for disposalshould be gained at an early stage such that the timescales and requirements(and the consequences of these) are properly understood and addressed.Early steps should include assessment of contaminant levels in the materialbeing considered for disposal (is sampling required) and investigation of wherelicensed disposal sites presently exist and their status in terms of the amountand type of material they are capable of receiving.NOTE In some circumstances it might be possible for a new disposal site to beopened (licensed); however, this typically requires substantial investment in terms ofcharacterization of potential locations, and consequently timescales are long andoutcomes uncertain.