the basis that the Red Crag is a Secondary A Aquifer, its sensitivity is considered to be medium.
Scenario 1: Pre-installed ducts 86.
The only intrusive works that would comprise the excavation of jointing pits as ducts would already be in place for the cable installation. Themagnitude of the impact of the construction works at landfall is therefore considered to be negligible and the significance of the impact would be negligible.
Scenario 2: Trenching and ducting 87.
The cable installation at the landfall will be completed via HDD. In this scenario the drilling would be carried out at the time of cable installation and would include more, or larger, jointing pits and therefore more intrusive works would be carried out. Given that there will be no dewatering required as part of the HDD works, the magnitude of impact to groundwater levels is considered to be negligible and therefore potential impact to the groundwater resources is considered to be negligible.
88. Drilling fluid would be used during the drilling process comprising wet bentonite- type slurry. The impact from the accidental loss or spillage of drilling fluid may occur during drilling but is likely to be minimal in volume and any potential impacts limited in spatial extent, therefore, it is considered unlikely to be detrimental to the background groundwater quality. The impact of drilling fluid loss is considered to be temporary and of low magnitude. The significance of the impact is considered to be minor adverse.
21.6.1.3.2Onshore cable route and Converter Station 89.
The geology beneath the onshore electrical transmission works fromlandfall to Great Bealings predominantly comprises granular sand and gravel type material within the Kesgrave Catchment Subgroup, Alluvium or Red Crag. All these deposits are classed as Secondary A Aquifers. This area does not lie within a groundwater SPZ although three private abstraction licences lie within the Great Bealings area, licensed for agricultural purposes. The sensitivity of the groundwater in this area is considered to be medium.
90.
From Great Bealings westwards towards the converter station the surface geology comprises mostly chalky till (clay) with Alluvium and locally exposed Chalk in the Gipping Valley. The till (Lowestoft Formation) is classed as an Unproductive Strata, whilst the Chalk is classed as a Principal Aquifer. The cable route passes through three SPZs. The sensitivity of the groundwater from Great Bealings westward is considered to be high.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 21 Water Resource and Flood Risk Page 34
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