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Omfang og konsekvenser af forskellige strategier for håndtering af forurenede sedimenter

Resume and conclusion

This project compiles and uses the results from a number of the Danish EPA projects carried out in the last couple of years, concerning sediment and dredging. The aim is to estimate the economical extent and the consequences of different strategies for discharge of sediment with a potential risk of containing polluted substances. This mainly concerns material from cleaning up harbours.

Several estimates on dredged material are compared: DHI (2000), Association of Danish Harbours (2001) and the Danish EPA (2001). Up to 750,000 tonnes of about 3 million tons dredged material will be in the category 'potentially polluted'. This estimate has been used as basis for the calculations in the project.

Based on the ATLAS database, it has been calculated where in the Danish waters the background levels are for the metals mercury, cadmium, lead an copper, for tributyltin and for one PAH (benzo(a)pyrene). The median value has been used as an term for where the central point of the measurements is.

A number of strategies can be used in the assessment of the degree of pollution of the sediment i.e. criteria for load and toxicity, but as basis for the consistency assessment it has been decided to use background concentrations for the substances in the environment with two limit values as recommended in the international conventions.

Table 4. Background concentration and action levels for six compounds.

The three ways of discharging are: ordinary dredging, dredging under controlled conditions and landfilling. A number of activities are linked to the way these discharges are carried out. Each activity has been divided into operational units which are priced according to former reports on the subject, information from the follow-up group and from contact with the trade and the ports. Following this, the total cost on a national basis has been estimated for a number of scenarios.

Table 5. Dredging Expenses.

The cost of the discharge methods must be seen in relation to the minimum price being the price for dredging anyway. Furthermore, material is already being stored in depots. According to Association of Danish Harbours (2001) this amounts to 278 m³.

To illustrate the costs in different harbours estimates have been made for a small harbour, a large harbour, traffic harbour, fisheries harbour and a marina. The following harbours, where the concentration of relevant substances in the sediment is known or can be estimated, has been chosen as examples: Bagenkop harbour, Århus harbour, Odense harbour, Århus fisheries harbour and Marselisborg marina.

Table 6. Expenses for removal of habour sediment in selected harbours.

Variations of discharging methods have also been estimated in the report such as cleansing of harbour sediment with mobile or permanent facilities. For some harbours, different detail scenarios have also been estimated.

The main conclusions are that the use of the antifouling substance, tributyltin, means that the concentration of the substance will exceed the general level of background concentration in the environment twice which has been an guideline for dredging in Denmark. Exceeding costs in connection with cleaning the sediment from harbours where this limit is not met will amount to between 33 and 361 million DKK pr. year. Regional depots, cleaning of sediment, use of different means of dredging under more stringent conditions can limit the total costs, compared to a possible depositing of the polluted sediment. For smaller harbours and marinas, the costs of transport and depositing or cleaning may constitute the major part of the costs of dredging.

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Version 1.0 Januar 2006, © Miljøstyrelsen.