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Pollution caution for gas pipe crossing

ENVIRONMENTAL PROTECTION was high on the agenda when laying of Transco's new Treales to Burscough high pressure gas pipeline reached the River Ribble near Preston, Lancashire.

A number of provisions were made for the directional drilling contract which involved forming a 640m long, 1.5m diameter bore under the river. Hole cuttings were recovered from the entry and exit pits and the drilling fluid cleaned for recirculation via a temporary line running back across the river. A lagoon was also built to hold, and recover if necessary, any contaminated mud returns from where the drill passed through an old refuse tip on the north bank.

Contractor Smit Land & Marine was brought in by main contractor McAlpine- Preussag to drill the bore, but before work could start, substantial layers of gravel on both banks had to be grouted. The drilling profile, optimised using data from extensive geotechnical and geo- physical investigations, was set at a depth to avoid affecting flood banks on either side of the river. Once the bore was completed through the underlying sandstone, the 1.1m diameter pipeline was pulled through.

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