Page 92 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
insignificant impact. The cables are likely to be buried in soft sediment areas and placed
directly on the seabed and covered with protection in areas where the cable cannot be buried.
Overall, therefore, the level the exposure to change is negligible to low, resulting in an
insignificant impact.
5.2.2.3 Toxic contamination (sediment release)
In areas being excavated or disturbed for the installation/removal of tidal stream turbines,
cables or offshore substations there will be an increase in suspended sediment concentrations
during the period of the activity. Where this occurs then the potential also exists for the
mobilisation and release of sediment-bound contaminants into the water column. However, as
outlined in water quality (Section 4.3.2.3) and sediment contamination is considered only likely
to be evident in areas close to the coastline of industrial locations or in coastal areas where
water and sediments have been subject to historical contamination. . Furthermore, the majority
of seabed sediments in Alderney waters are coarse-grained (see Section 4.1), and the levels of
sediment-bound contaminants associated with these are likely to be negligible. Overall, it is
considered that for the installation and decommissioning of the tidal stream turbines and
offshore substation the exposure to change is negligible to low, resulting in an insignificant
impact. For cable routeing the exposure to change is considered to be low, resulting in an
insignificant impact.
5.2.2.4 Mitigation
Given that none of the impacts on pelagic ecology are significantly adverse (i.e. moderate or
major), no mitigation measures are considered to be necessary.
5.2.2.5 Residual impact
Given that no mitigation measures are required for pelagic ecology, the residual impact has not
been assessed. The significance of potential impacts has been estimated and summarised in
Table 13.
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