TBT’s TREATMENT AND DISPOSAL
Monday 24 September @ 14:00hrs
A HALF DAY MEETING ORGANISED BY THE CENTRAL DREDGING ASSOCIATION, BRITISH SECTION
Institution of Civil Engineers, One Great George Street, Westminster, SW1P 3AA
Treating and disposing of TBT-contaminated dredged material - defining the problem
Steve Challinor, Technical Director (Environment) Royal Haskoning
The situation concerning the TBT contaminated sediment at Falmouth Dockswill beused to define the problem associated with treating and disposing of dredged material. In essence, the problemwill highlight the difficulty inidentifying environmentally acceptable, technically feasible and cost-effective treatment and disposal. The paper will describe the TBT concentrations and distributions in the in situ sediment and will describe the potential environmental issues influencing treatment and disposal. Based on work conducted in the late 1990s, the paper will introduce the factors that influence the viability of different treatment methods (thermal, biological, chemical and physical techniques) and disposal options (sea disposal, landfill, confined disposal on land and in water). These factors include the distribution of TBT across grain sizes, the efficacy of the treatment methods in reducing contamination to environmentally acceptable levels, the complications caused by the presence of other contaminants, the logistics of handling and transporting large quantities of dredged material, the availability of suitable disposal facilities (eg landfill), etc.The latest proposals for capital dredging the approaches to Falmouth Docks will be used to highlight the potential magnitude of this problem. A preferred option will besuggested.
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Understanding the practical issues of TBT contamination and remediation
Dr Mike Waldock, Cefas
By the mid 1990’s TBT contamination of sediments became the most common reason for refusal of a licence for disposal of dredged material. Analysis of samples provided extraordinarily high readings with some values up to 100ppm. The distribution of concentrations in harbours was patchy and pointed to paint material entrained in sediments. The biological availability of this form of TBT was not well understood and the implications for disposal and/or remediation were not clear. Defra sponsored a programme with Cefas between 1999 and 2002 to examine a range of issues associated with availability and remediation to inform the risk assessment process. This presentation provides some of the research outputs.
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Cleaning up Cornwall
Ian George, Technical Director, Hyder Consulting (UK) Ltd
Large numbers of small and big harbours are contaminated with TBT. This is thwarting development and jeopardising economic competitiveness at a time when many waterside communities are suffering from lack of investment. Two award winning projects, both similar and different, demonstrate practical TBT stabilisation and solidification of sediments for beneficial use. Both projects would not havehappened with the full support of the statutory consultees, a proactive project team and flexible clients. Both sites are now going from strength to strength.
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Tyne Capping Trial
Dr Jonathan Wilson, Envirocentre Limited
Research over the past five years has focused on identifying the best practicable environmental option for the treatment and/or disposal of dredged TBT contaminated material from the Tyne Estuary. A risk-based approach utilising a matrix of environmental, economic, social and legal factors was developed to assess and rank viable options.The technique allowed the analysis of multiple criteria and proved a powerful decision making tool.
The risk-based approach has been used in the selection of preferred management methods for TBT contaminated dredgings and resulted in a trial to dispose 60,000 cubic metres of contaminated Tyne Estuary sediments to an existing sea-disposal ground capped with a layer of fine sediment to isolate contaminants from the environment overlain with sand to protect against erosion.
This trial is the first confined sea-disposal operation undertaken in the UK and aims to demonstrate the effectiveness of the technique and allow the development of best practice guidance. The rational for the trial was founded on US Army Corp of Engineers guidance. The trial has been undertaken over the past two years with an extensive monitoring program allowing an evaluation of the technique.
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Developing a UK Strategy For Managing Contaminated Marine Sediments
By Dr Kevin Black, Partrac Ltd., Glasgow
Contaminated marine sediments are widespread in UK coastal waters, and currently there is no consistent strategy within Government for their management on an integrated basis. The Department for Environment, Food and Rural Affairs (DEFRA), in conjunction with Natural England and the Crown Estate, have recently funded a 3-year project to develop a strategy to manage contaminated marine sediments in UK waters which will:
- Make the assessment of all dredged material disposal options a transparent process which takes into account the principles of sustainable development on a case-by-case basis.
- Consider the impacts of moving contaminated marine sediments from their location within the marine environment.
- Draw together existing work on best practice using all available sources of information and organisations involved in contaminated sediment management.
- Examine the current legislatory process to enable the best disposal option to be used.
- Define the scale of the problem including where the contaminated marine sediment occurs and where and how it is currently disposed.
This presentation summarises the background to the inception of this project, and describes in detail the component 6 Work Packages designed to underpin the strategy.
CENTRAL DREDGING ASSOCIATION
BRITISH SECTION
TBT’s TREATMENT AND DISPOSAL
Monday 24 September 2007 @ 14:00hrs
A HALF DAY MEETING ORGANISED BY THE CENTRAL DREDGING ASSOCIATION, BRITISH SECTION
Institution of Civil Engineers, One Great George Street, Westminster, SW1P 3AA
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Please return to: Sophina Khan