Chapter 19 Soils, Geology and Ground Condition identified a number of potentially contaminated sites and landfills within 250m of the onshore electrical transmission works. Two sites were identified as active landfills (Bamford Dairy and Blood Hill). Bamford Dairy is recorded to lie within the works footprint. Two historical landfills (Sandpit Tuddenham St Martin and Culpho Hall) are also recorded to cross the cable route. Where these sites are crossed there is the potential that contaminants could be remobilised in the groundwater and/ or the protective clay layer (till) above the chalk could be removed permitting the transmission of contaminants to the aquifer below. The creation of a pathway is considered to be permanent and potentially widespread. The release of leachates from landfills or other potentially contaminative materials into either a Secondary A or Principal Aquifer is considered of high magnitude. The significance is therefore considered to bemajor or moderate adverse. Additional mitigation to reduce the impact significance is described below in Table 21.14.
97.
The use and storage of machinery, fuels, cement based products, such as concrete and grout etc. should be monitored and maintained to reduce the risk of spillage. The impact of accidental spillage is considered to be localised to the areas where potential contaminants will be stored, such as compound areas. The impact from spills and leaks is considered to be temporary and of low magnitude resulting in a generally minor adverse impact except in the Gipping Valley chalk area where the impact is likely to be moderate adverse.
98.
The foundations at the converter station would either be ground-bearing or piled based on the prevailing ground conditions. A CoCP, including method statements including for groundwater pollution, would be agreed with the relevant local planning authority prior to construction.
Table 21.14Mitigation measures for impact to groundwater Scenario 2 Mitigation measures
In order to reduce the potential impacts to groundwater resources and groundwater quality the following mitigation should be undertaken: Minimise the length of time that trenches are open to reduce the requirement for dewatering; and
Periods of low flow will be chosen to carry out construction works wherever practicable.
In order to reduce the impacts to groundwater quality from the creation of permanent pathways between potentially contaminative sites and the underlying principal aquifer, and the impact of spills and leaks, the following activities should be undertaken: The removal of superficial clay deposits should be minimised wherever possible; Where landfills or potentially contaminated sites are crossed the cable and duct surround should be appropriately designed to prevent the transmission of contaminants, for example, where appropriate, the trench could be backfilled with a low-permeability
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 21 Water Resource and Flood Risk Page 36
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