This June 1999 Environment Agency Report “Tees Estuary Present & Future” is I guess a well read report by those in the know, but on pages 59 and 103, it makes statements which are highly relevant for what is going on now. But it doesn't appear to reference the data behind it, apart from talking about using the regular measurements - on a quick scanning the ones related to Tioxide license which include water and sediment both at Greatham and in other places if still made could give direct evidence of changes caused by the Teesworks operations.
Page 59 says Basically fine to dredge where you are already dredging (i.e. navigation channels) but “great care must be exercised if dredging is planned in such areas to prevent redistribution of pollutants or re-suspension of sediment in the water column.” If you mustn't allow re-suspension of sediment then I can't see how you can then dump the dredged material at sea.
Page 103 says “Dredging and excavation of land contaminated by earlier industries can release a flush of pollutants. The only effective eradication may be their physical removal.” Once again this isn't just banging pilling into the bank or dumping at sea.
59: Dredging
Dredging at the sea-bed takes place to create and maintain channels for navigation and to extract minerals - mainly sand and gravel - from the marine environment. Dredged material from the Tees Channel continues to be disposed of at a site three miles offshore and this has been the case for some hundred years. The sea disposal point is vital in maintaining the marine sediment budget.
Potential environmental damage can ensue from dredging which is not properly managed. Studies have shown that present concentrations of heavy metals in the dredged, navigable channel are close to natural background concentrations. However, less disturbed locations are likely to have much greater concentrations of contaminants as a direct consequence of the industrial history of Teesside. Hence great care must be exercised if dredging is planned in such areas to prevent redistribution of pollutants or re-suspension of sediment in the water column.
103: Heavy Metals
Compounds containing heavy metals such as Cadmium, Mercury, Lead, Zinc, Chromium, Copper, Vanadium and Arsenic have been discharged to the Tees over the last 100 years, or leached from past deposits of solid waste on land adjacent to the river. Since heavy metals have a low solubility in water, they tend to be absorbed on to clay and organic particles and are deposited with fine sediment. Dredging and excavation of land contaminated by earlier industries can release a flush of pollutants. The only effective eradication may be their physical removal.