Geoscience Reference
In-Depth Information
importantly, (iii) the criteria by which perform-
ance will be measured.
forming action levels, the philosophical approach
taken is to use sediment chemistry to provide
an estimate of background metal concentra-
tions for Action Level 1 (Table 10.4). The deriva-
tion of Action Level 2 concentrations has been
guided by ecotoxicological information from the
literature, applied to concentrations in samples
sent in support of applications. Limited eco-
toxicological data are available, and most such
work has been done in North America (Burton
2002). Work is ongoing to derive background
'reference concentrations' for England and Wales,
so the concentrations given here are likely to
be revised. In Europe, under OSPAR, there is
no consistent approach taken; for example,
countries analyse different size fractions, some
countries may digest their samples only partially
and others digest samples fully using hydrogen
fluoride. Although this largely relates to coastal
and estuarine sites, it is indicative of some of the
problems involved, which could be applicable
to shelf environments.
There are also concentrations that are used
to assess sediment recovered in post-disposal
monitoring programmes, including those for
metals (e.g. Rowlatt et al. 2002) and for organic
compounds. Environment Canada has a series
of lower 'Action Levels' (London Convention
2005) for sediments collected during monitoring
programmes, which form part of an integrated
assessment procedure (Table 10.5). If sediments
are below the lower action levels for contami-
nants and pass all biological tests, no further
action is required. If levels of contaminants or
biological test results demonstrate a cause for
concern, however, then:
1
compliance is verified with the terms of the
permits issued since the site was last monitored;
2
potential sources of pollutants are checked
and further site characterization undertaken.
Cursory benthic community surveys can be
used as a general sediment quality indicator, but
the overall assessment of the disposal site con-
siders all information available from physical,
chemical and biological monitoring.
Within Europe, international co-operation on
such issues is not finalized, but the indication
is that monitoring of disposal sites should aim
10.4.6 Contaminants and sediment quality guidelines
As part of an assessment of environmental impact,
many countries have developed Sediment Quality
Guidelines, which are used to inform decisions
taken about sediment management (Chapter 1;
Wenning et al. 2005). A number of legislative
drivers require consideration of the potential
impact of contaminated sediment on aquatic
environments, including, in Europe, the Habitats
Directive and the Water Framework Directive.
The guidelines are used to assess the quality of
material that may be dredged (mostly from
harbours and coastal waters) and the quality of
sediments (e.g. dredge spoil) placed into the shelf
environment. In assessing dredged material and
its suitability for disposal to sea, defined concen-
trations of contaminants ('Action Levels') are
not generally used as a simple pass/fail test, but
rather are used as part of a 'weight of evidence'
approach (CEFAS 2003). This reflects recent
weight-of-evidence approaches to environmen-
tal management of sediments, whereby multiple
lines of evidence concerning ecological assessment
are used as an aid to decision making (Chapman
1986, 1996; Burton 2002). One relatively well-
developed approach to setting sediment quality
criteria is that of Long et al. (1995) and Long
& MacDonald (1998) in the USA. A statistical
approach matches biological and chemical data
from laboratory and field studies in North
America, and from modelling work, and the tech-
nique has since been developed to set sediment
quality guidelines in a number of countries,
notably the USA, Canada and Hong Kong.
In the UK, applications for the dredging and
disposal of contaminated material must con-
sider alternative options, including placing the
material in landfill, 'capping' it in the marine
environment and forming a new reclamation
site beneath which the material is placed (i.e.
an engineered new site). Much related research
has been performed by the U.S. Army Corp of
Engineers (DOER 2005). On occasion, high costs
can lead to a further option, of doing nothing. In
