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
Docks will be used to define the problem associated with treating and
disposing of dredged material. In essence, the problem will highlight the
difficulty in identifying 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 be suggested.
…..
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.
…..
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 have happened with the full support of the statutory
consultees, a proactive project team and flexible clients. Both sites are now
going from strength to strength.
…..
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.
……
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
Institution of Civil Engineers
1 Great George Street
London
SW1P 3AA
Te: 020 7665 2229 Fax: 020 7799 1325
Sophina.khan@ice.org.uk