Scotch and the rocks
Borehole offers effluent solution
Fraught with difficulties
The Sound of Islay is a fast flowing tidal waterway separating the Islands of Islay and Jura. More than 140-feet deep, the Sound contains tidal currents which frequently exceed 10 knots. Traditionally, discharge outfalls were short - typically less than 30 feet in length - exiting at low-tide water levels. Attempts to place long outfalls on the sea bed have been fraught with difficulties in construction and survival; severe damage or destruction by the sea in less than a year from installation is the rule.
Longbore was contracted by UDV (Distilling Ltd) to install an outfall to exit 500 feet from the shoreline at a depth of 100 feet, by directionally drilling a borehole from an entry point 500 feet inland and 100 feet above sea level. Not easy, particularly when:
The attraction of having a high velocity, deep tidal stream to enhance the effluent dispersion was challenging for completion of the outfall pipeline. The 'slack water' time was less than 20 minutes at high and low tide, so diving operations were extremely restricted. This time restriction and water speed eliminated the ability to pull back the pipeline from the exit so it had to be inserted under compression into the borehole. Longbore technology enabled the welded 1,100-foot-long pipeline to be inserted in just 30 minutes.