51.


The dominant bedrock beneath all areas of site, albeit at depth in most places, is the Cretaceous Chalk which is defined by the Environment Agency as a Principal Aquifer. This rock has secondary permeability (fracture flow), can provide a high level of water storage and supports water supply and base flow to rivers.


52.


Overlying the Chalk Principal Aquifer across the majority of the eastern section of the cable route is the Red Crag formation, which is described by the Environment Agency as a Secondary A aquifer. As published by the BGS (2000), the development of the Crag Aquifer is limited due to:


 The unconsolidated nature and poor sorting of deposits;  The variable and unpredictable yields;  High iron concentration in the groundwater; and  Problems with relatively high concentrations of manganese and nitrate.


53. Where the Thames Group and Harwich Formations are present along the route the aquifer designation is classed by the Environment Agency as unproductive strata.


54. A summary of the aquifer designations for each stratum is presented in Table 21.9 below.


Table 21.9 Summary of Environment Agency Aquifer Designations Stratum


Description Alluvium


Marine and Coastal Zone Deposits: Mud


Head


Superficial Deposits


River Terrace Deposits (undifferentiated)


Glaciofluvial Deposits Lowestoft Formation


Kesgrave Catchment Subgroup


Bedrock Red Crag Formation


Variably sandy, silty Clay


Mud


Stony sandy clay and clayey sand


Sand and gravel


Sand and gravel Stony, sandy clay


Sand and gravel Sand Aquifer Designations Secondary A Aquifer Unproductive Strata Secondary A Aquifer Secondary A Aquifer


Secondary A Aquifer Unproductive Strata


Secondary A Aquifer Secondary A Aquifer


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 21 Water Resource and Flood Risk Page 22


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