Question to the Department for Transport:

To ask His Majesty's Government, further to the Written Answer by Baroness Vere of Norbiton on 21 October (HL2420), what is the source of contaminated water that has been identified in the cofferdams and necessitated an application to vary the Water Treatment Plant Permit.

The water within the cofferdams comes from lake water ingress through the sides and base of the cofferdams. The quality of this water is affected by interaction with lakebed sediments and the concrete plug in the base of the cofferdam while it cures. It is this water that is tested, pumped out, and may require treatment before it is of a quality to be returned to the Colne catchment. This water treatment, via the Water Treatment Plant, required a variation to the permit. The piling for the Colne Valley Viaduct is largely complete and the extensive monitoring of groundwater around all piling works and cofferdams has detected no contamination issues in the water environment related to construction works within the Colne Valley.