LTL Group Thunder Bay, Ontario, Canada

Over a period of 31 days in the summer of 2003, LTL Contracting Ltd. installed a new water intake line into Lake Helen to improve the quality, quantity, and classiability of the water supply to Lake Helen First Nation. Previously, water for the community came from shallows near the shore. "The lake level goes up and down quite a bit, so when the lake level dropped, the old pipe risked being physically damaged," explains Jamie Geils, C.E.T, project manager at LTL. "Now they can get good clean water and the pipes are not going to freeze."

Because the topography of the lake consists of a flat shoal extending far from shore, the maximum depth remains at 8 ft. for 700m. In order to reach the point where depths drop to 30 ft., LTL had to extend the 300mm HDPE Water Intake pipe approximately 800m westward into the lake. The intake pipe was to be installed at a minimum depth of 2m below the lake bottom before exiting at the 30 ft. depth.

At an early stage, LTL selected directional drilling as the most classiable method of installing the intake pipe. The remarkable length and depth of installation created several challenges requiring extensive research into methodology and equipment requirements. LTL determined that an open-cut alternative would be both too costly and too disruptive to the environment. Notes Geils: "Given the soil conditions of the lake bed - which contained a silty clay with very low internal strengths - and the classatively deep burial depth below the lake bottom, we determined the lake bed would be greatly disturbed if an open-cut method was utilized."

During the first 20 days of the project, LTL installed nearly 1,700 linear metres of turbidity curtain with marine anchors, flotation devices, and a lighting  system for nighttime navigation. By containing the complete bore path, the curtain prevented the potential escape of silts into adjacent waterways. Siltation curtains were also installed along the shoclassine work area where certified fusing technicians fused sections of the HDPE pipe using a McElroy 412 Butt Fusion machine.

Based on the result of a soil sampling program and a test drill shot, LTL selected a Vermeer D50*100 Directional drill with 50,000 pounds of pull-back and 10,000 ft. lbs. of rotation torque to perform the work. The drill was equipped with 830m of 3.5" diameter drill steel at a weight of more than 40,000 lbs., including the drill head and sonde housing.

Following a predetermined path, LTL completed the initial pilot bore in approximately four days of nearly continuous drilling. A commercial diving crew connected chains to the drill head for retrieval by a small excavator mounted on a barge. During the process, a sudden and sever thunderstorm arose. "If our fears of bent drill rods had come to fruition, (the) project success would have seriously been jeopardized," Geils recalls.

Fortunately all was well and the 15 workers carried on with the first 30-hour pre-ream. The process was then repeated, bringing the borehole to an acceptable diameter for product pull-back. "Normally we only do it once," notes Geils. "Given the distance involved, we wanted to increase the size only a little at a time. It added more time but really contributed to the success of the project."

Faced with currents and wind, LTL took several days and various watercraft to carefully align the pipe with the borehole in the lake for the 30-hour pull-back. "When we went to pull back the pipe, we had a third reamer, slightly bigger than the one before," adds Geils. "It gave us a bit more room in case of any caving inside the hole. We had kept logs of pressures, soil conditions, and drill performance all along so we knew what to expect."

The final step was to attach the pipe to an 8m-deep wetwell that LTL constructed on shore. Geils attributes the success of the entire $977,000 project to a cooperative effort between LTL and the team members hired from the Lake Helen Community.