21.6.2.1 Impact 1: Impact to Groundwater and Surface Water
21.6.2.1.1 Landfall and onshore cable route 92.
Routine maintenance works would be required during the operational phase; however, this access would be via jointing pits or kiosks, and any excavation will be limited to the area around those, and therefore would result in minimal disturbance. In addition jointing pits will be located at least 10m from watercourses and at a maximum depth of 2.5m. Therefore it is believed unlikely that there is any pathway for impact to groundwater levels and quality and surface water flows and quality from routine maintenance.
93.
In the event of a cable failure, it may be necessary to re-excavate the cable trench and replace / repair the faulty cable along limited stretches. At major water crossings, the cables installed via HDD and would be within ducts. Therefore if cables need to be removed at these points there would be no interaction with the watercourse itself. Works would be based around jointing pits which would be located 10m away from any watercourses. Therefore for major water crossings it is considered that there is no pathway for impact during operation. This is also the case for minor water crossings under Scenario 1.
115. For smaller water crossings where open trenching takes place under Scenario 2, if repair works are required, the mitigation measures outlined for the construction phase activities in section 21.6.1 would be adhered to, in order to reduce or minimise any potential impacts to an acceptable level. It is considered that the impact significance of this would not exceed minor adverse at the location affected. Mitigation would also be employed to ensure spills and leaks are avoided or contained as described in Table 21.14.
21.6.2.1.2Converter station 116. There are no watercourses at the converter station location and therefore there would be no direct impacts on surface waters. Mitigation would also be employed to ensure spills and leaks are avoided or contained as described in Table 21.3 and Table 21.14. In addition note that the design of the converter station compound will incorporate a sustainable drainage system (SuDS) and runoff will be managed to maintain greenfield runoff rates. In addition, there will be sufficient site attenuation for rainfall up to 1 in 100 year probability events, plus a 30% allowance for climate change.
21.6.3 Potential impacts during Decommissioning 117. This section describes the potential impacts of the decommissioning of the onshore electrical transmission works with regards to impacts on water resources and flood
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 21 Water Resource and Flood Risk Page 41
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