Most marine dredging for aggregate takes place over five kilometres away from the immediate vicinity of the coast. There is little extraction closer to the coast. The total amount of sand and gravel extracted for use as aggregate from all licensed areas in UK waters over the past 10 years is about 253.3 million tonnes. It is not possible to estimate with any certainty how much can be removed within safe environmental limits since the total size of the resource is not yet known. In addition, impacts on the sea-floor, marine currents and waves, habitats and uses of the sea all need to be assessed in detail, on a project-by-project basis, to establish whether any individual proposal is environmental acceptable. Each licence application is subject to an environmental impact assessment which includes a coastal impact study. This is the subject of careful analysis and wide consultation and, if necessary, additional investigations before a decision is taken. All licences that are issued by the Crown Estate are subject to conditions specified by Government to make sure that any environmental impacts are minimised. Licences are time-limited so that the position can be reconsidered if further dredging is proposed.