Impact
materials, specifically accidental spillages and discharges of grey water.
Key design parameters forming the realistic worst case scenario Rationale
1. Maximum number of installed structures would be 180. 2. Maximum average number of visits by large vessels per annum conducting “big operations” would be up to 730.
3. Maximum average number of visits by service vessels per annum52.
4. Maximum average number of windfarm support vessel trips to site per annum4,015.
Total maximum number of visits by vessels per year of operation 4,797
Access to installations would be by a variety of vessels and helicopters.
Large jack up vessels may be required to operate for significant periods to carry out maintenance work associated with the larger components of the windfarm e.g. wind turbine blades or substation transformers. Smaller specifically designed service vessel would carry out the smaller operations whilst windfarm support vessels would transport personnel to the site for small scale maintenance procedures
Therefore, the worst case scenario provides for the maximum level of operational activity and therefore, the highest likelihood of an incident occurring due to increased vessels / activities.
Decommissioning
Impact 1: Deterioration in water quality due to re- suspension of sediments associated with the removal of foundations.
Impact 2: Deterioration in water quality due to re- suspension of sediments associated with cable removal.
The worst case scenario would involve gravity base foundations with a 60m diameter base. It is anticipated that upon decommissioning foundations would be removed at or just below the surface.
Cables would be cut off where they enter wind turbines, converter and collector stations and buried cable would be left in-situ.
Note: that there would be up to two cables to interconnect the proposed East Anglia THREE and East Anglia ONE projects. The cables would either be two cables, subject to detailed design and future technology developments. Each would be up to 90km in length. The locations where these interconnections join the East Anglia ONE electrical infrastructure would be identified following detailed electrical design and would be dependent upon the location of the East Anglia ONE converter stations. These cables have not been assessed as part of the worst case and once interconnection cable routeing has been determined they will be added into the assessment.
Likely to be of a similar magnitude to Construction Impact 1
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 8 Marine Water and Sediment Quality Page 8
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