Scenario 2: Trenching and installing ducts 74.
At the landfall, HDD is planned to take place bringing the cables onshore via tunnelling (EATL has undertaken intrusive ground investigation studies which confirms HDD is feasible at all locations). The cable installation will start at an appropriate distance from the sea cliff and to an appropriate methodology to be agreed with the relevant planning authority in consultation with Natural England. The optimum scenario would be to undertake a ‘long’ drill which would surface the cables a significant distance from the base of the cliffs, thus avoiding the designated area entirely. The ‘short’ method, and worst case scenario, would surface the cables potentially within the intertidal zone. In this situation a temporary haul road would be required to take traffic up and down the cliff face to access the foreshore.
75.
The changeable loading of the cliff face by the placement of a haul road and ramp could impact on its stability. The sensitivity of the geological receptor at the landfall is considered to be high, given its status as a SSSI but reflecting that the interest feature is not present at this location. Temporary construction of a haul road against the cliffs is considered to be a potentially low magnitude as there would be no changes to the protected geological attributes of the designated site. On this basis, the impact significance at landfall is considered to be moderate adverse. Additional mitigation is discussed in Table 19.17 above. Following implementation of the mitigation measures described above, the overall significance of the impacts to designated geological receptors is considered to be minor adverse.
76.
The presence of compounds and mechanical excavators brings with it the hazard of spills and leaks. Compound areas will be set inland of the cliff face away from the sensitive geology and outside of the designated area. One haul road and access ramp will be constructed for the duration of the works and removed following completion. Given the limited volume of potentially contaminating materials likely to be stored and adherence to the embedded mitigation these impacts are considered to be temporary and of low magnitude, giving a negligible impact.
77.
Excavation of HDD starter pits will disturb soils and temporarily open the soil structure, potentially increasing the likelihood of erosion or settlement. All HDD works will be set inland of the cliff face outside of the area of designated geology therefore the impact of excavation and disturbance of soils is considered to be low magnitude.
78.
In general the drilling and excavation works will be set outside of the Bawdsey Cliffs SSSI and therefore it is considered that the works would, following mitigation, result in a no significant impacts to the status of the SSSI.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 19 Soils, Geology and Ground Condition Page 36
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