Dewatering, using appropriate sediment control techniques and/or trench supports may be used to facilitate safe excavation. If pumps are used, the discharge hose will be directed through a filtering medium to remove silt, before the pumped water is allowed to percolate back into the watercourse or to ground if appropriate;
The pumped water will be filtered, where practical, to remove sediment before being discharged back into the watercourse. Straw bales will be used to remove sediment;
Backfilled materials will be as erosion resistant as original bed material if different from original bed material;
A site investigation will be undertaken to determine the type of fill material, depth of fill, presence/condition of groundwater within landfill, presence of any lining system. The information obtained during site investigation will inform appropriate design of trenching to prevent creation of pollution pathways;
Use of low permeability material (e.g. clay plug), upstream and downstream, of sites of potential contamination and landfills to break potential flow of contaminants (within groundwater) along the cable route to watercourses;
Works will be thoroughly planned and controlled in order to minimise the risk of pollution;
Appropriate treatment methods will be adopted prior to discharge of the water from any land drains uncovered during the construction phase.
111. Following implementation of the mitigation measures described above, the overall significance of the impacts to designated geological receptors is considered to be minor.
21.6.1.4.1Converter Station 112. There are no watercourses at the converter station. The proposed surface water drainage scheme will be designed to meet the requirements of the NPPF by managing construction runoff to existing greenfield runoff rates and preventing sediment laden runoff entering nearby streams. On this basis, there would be no impact to surface water flows or levels at the converter station site. In order to mitigate potential risks to surface water quality at the converter station, mitigation as outlined in Table 21.15 (above) should be adhered to.
21.6.2 Potential impacts during Operation 113. This section describes the potential impacts arising during the operational phase of East Anglia THREE. Reference should also be made to Chapter 5 Description of the Development for full details of the operational phase.
114. The differences between Scenarios 1 and 2 of cable installation are related to the construction phase only, and therefore the impact assessment for operation is the same regardless of installation methodology. The only difference would be the number of jointing locations, with 61 locations in Scenario 1 and 48 under Scenario 2.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 21 Water Resource and Flood Risk Page 40
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