Two Platforms, Two Shore Approaches, Two Lines And A Hurricane

By Angus W. Stocking | December 2013, Vol. 68 No. 12

The power supply for Virginia's densely populated Middle Peninsula Area, on the Chesapeake Bay, is currently adequate but somewhat fragile; a single 115 kV line extends southward from the Harmony Village Substation of Dominion Virginia Power (DVP). The non-redundant power supply was at risk for long interruptions and local demand threatened to outstrip supply.

Accordingly, in 2010, DVP obtained approvals to serve the region with a new, 230 kV power line extending from their Yorktown Power Station. But approvals are one thing and actual achievement is another; installing the line was a significant technical challenge.

For one thing, about 3.5 miles of the historic York River lies between the Yorktown Power Station and the Middle Peninsula. That mandated a very long river crossing and environmental conditions made horizontal directional drilling (HDD) the only feasible method. Actually, to supply sufficient power with redundancy, two parallel crossings were needed. DVP elected to tender the project on a design/build basis and contractor Mears Group was selected based on experience and innovative proposal. Mears commenced design work in 2010.

Conceptually, the solution proposed by Mears Group was simple. Two platforms, 7,300 feet apart, would be established. The north platform would be about a mile from shore and the south platform about half that. Both were to be located within the bends of the S-shaped right-of-way (ROW), so that the longest crossings of the project were straight. Line A would run from north and south shore staging areas to the nearest platforms and Line B, offset 20 feet from Line A, would be run next. HDD equipment was then shifted as needed and the long platform-to-platform HDD crossings would take place.

The proposed product to be installed was actually a bundle of two pipes – eight-inch steel conduit for the copper cable and the high-pressure dielectric fluid needed to keep it cool; and three-inch HDPE for a fiber optic communication line.

"Anything over a mile is notable when it comes to river crossings," says Craig Prout, senior project manager for Mears Group, "But it wasn't the length alone that made this project unique; it was the length combined with all the other factors."

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