To remove and replace seven 50-year-old, oil-filled cables under Lake Champlain that connect terminals in Plattsburgh, N.Y., and Grand Isle, Vt., was a delicate, difficult project.

Adding four new 230-kilovolt transmission lines—which operate at 115 kilovolts and use distributed temperature sensing and fiber optics for improved monitoring—came first. This entailed installation of 1.7 miles of cable over land and at depths of 200 ft in the lake as well as construction of transition stations and overhead structures.

Landside work installed cables by direct burial and trenchless drilling. The transition from land to lake employed horizontal directional drilling. In the water, a jet plow towed by barge and operating 30 ft below the surface installed cable 4 ft into the lake bottom.

Removing the old lines, which were at risk of leakage, was next. Crews purged the oil and then reeled the cables onto a barge, cutting them into sections for smoother recycling. The team also removed old transition stations and restored the natural habitat.

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