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Sediment Quality

The PLA require sediment at dredging areas to be analysed on a two to three year cycle as part of the dredging licensing process. Cefas also undertake analysis of sediments within the estuary as part of the FEPA licensing process, albeit only when disposal of sediments be required offshore. When a FEPA application is received by Defra, Cefas carry out analysis of the sediments in order to assess the nature and degree of any chemical contamination present.

The chemical characteristics of the sediments are described in terms of a range of chemical parameters that can be associated with sediment due to their low solubilties in water. Unlike water quality, there are no quantified UK environmental quality standards (EQSs) for in situ sediment quality. The only guidance for sediment quality is defined as “standstill (no deterioration)” and is required for most of the EC Dangerous Substances List 1 parameters.

In the absence of any quantified UK standards, the sediment quality data has been compared against other guidelines to provide a basic indication about the degree of contamination and its potential suitability for disposal. The two sets of standards are:

Sediment quality data within the study area is available for metals and organotins, polychlorinated biphenols (PCBs), and poly aromatic hydrocarbons (PAHs). In general, the sediment quality throughout the study area exhibits a varied degree of contamination from a variety of substances. Contamination levels however remain predominantly below the higher Cefas action levels and the higher sediment quality guideline levels.

For more detail on sediment quality, see Appendix B of the Baseline Document for the data tables.

Chemical Parameters

These include:

  • Heavy metals (arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc) and other metals (aluminium, boron, iron, manganese, selenium, silver and vanadium);
  • Organotins (Tributyl tin (TBT) and dibutyl tin (DBT));
  • Total petroleum hydrocarbons (TPH);
  • Polyaromatic hydrocarbons (PAHs) (USEPA 16);
  • Polychlorinated biphenyls (PCBs) including 25 congeners;
  • Ammonia; and
  • Sulphide

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