90. Whilst the majority of the structures would be transported to site having been pre- assembled or manufactured on land, it is likely that the use of grout would be required for all possible foundation types and cable protection may require pre or post-lay armouring using concrete for example. In addition, there is the potential for other substances such as grease or oil and antifouling paints to be accidentally released into the marine environment.
91.
EATL is committed to the use of best practice techniques and due diligence throughout all construction, operation and maintenance and decommissioning activities (please refer to section 8.3.3 for further detail).
92.
As the magnitude of the effect is difficult to assess, the assessment in this instance is considered in terms of the risk of a spill or other accidental pollution event occurring. Since control measures would be in place, the risk of a spill and associated adverse impact is considered to be of low likelihood and of a negligible significance.
8.6.1.5 Impact 5: Change inWater Quality due to works at the offshore export cable Landfall
93.
At the landfall location at Bawdsey the worst case scenario includes installation of four cables using HDD. Further information on the method of HDD installation is described in Chapter 5 Description of the Development.
94.
The ‘short’ HDD option may cause some disturbance when trenching and backfilling is needed in the areas of London Clay, further seaward in the intertidal or near shore zone. However, these effects would be highly localised and temporary in duration. The ‘long’ HDD option would cause minimal direct disturbance.
95. Depending on the installation option chosen, if the exit point of the HDD occurs within the sub-tidal or intertidal zone (as proposed with the ‘short’ method), a retainer (such as a cofferdam) may be required to create a dry area for cable jointing and to contain and retrieve the bentonite slurry mixture which is used in the HDD.
96.
The short HDD is expected to start 180m inland from the coastline with the break out in the sub-tidal. There would be no excavated material offshore and only minimal excavated material from the intertidal which would rapidly fall out of suspension. Therefore, the potential effects on suspended sediment concentrations in the water column in terms of magnitude are predicted to be negligible. Additionally, the designated bathing waters in closest proximity to the landfall site are situated 6km and 9km from the landfall location and therefore the sensitivity of the water is deemed to be low.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 8 Marine Water and Sediment Quality Page 30
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