Pebble gasline plan gels

Corps of Engineers decision sets overland route from Diamond Point to Pebble mine

Steve Sutherlin

Petroleum News

The route of a subsea and overland natural gas pipeline, from the lower Kenai Peninsula to the site of the proposed Pebble Mine site in southwest Alaska, appears to be taking its final shape due to a recent decision from the U.S. Army Corps of Engineers on a preferred development alternative for the proposed copper-gold-molybdenum-silver mine.

The Corps chose EIS Alternative 3 - known as the northern transportation corridor - as the least environmentally damaging practicable alternative or LEDPA for the proposed Pebble mine.

Under Alternative 3, the subsea Cook Inlet portion of the gas line would make landfall at Ursus Cove, near the proposed Diamond Point port location on Iliamna Bay, near Williamsport, on the west side of the inlet. From Diamond Point, the gas line would follow the northern transportation corridor overland to Pebble, buried in a trench adjacent to the road.

From Ursus Cove to Diamond Point port and on to the mine site, the gas pipeline would extend 165 miles. From Ursus Cove, the pipeline would be routed overland, northward to Cottonwood Bay. A 150-foot temporary construction right of way is proposed to allow for adjustment of the final route to accommodate variations in terrain.

Access for construction would be by barge landings from each end of the ROW. The ROW would shrink to a 50-foot permanent operations ROW following completion of pipeline construction.

The pipeline would come ashore at Diamond Point port, where natural gas would be fed to the port site power station and used for site heating.

Diamond Point is approximately 25 miles north of the Amakdedori port, which under the Alternative 1 variant of the EIS would have been the gateway to the Kokhanok east ferry terminal site. Under that scenario the gas pipeline would run overland from the Amakdedori port to the Village of Kokhanok, and from there it would continue under water across the bed of Iliamna Lake to the north shore.

The Amakdedori port would not be constructed under Alternative 3.

Alternative 3 designates an all land-based transportation route to connect the proposed mine site to a port site on Cook Inlet via an 85-mile double lane road located north of Lake Iliamna, which eliminates the need for ferry transport across the lake.

The northern transportation corridor would serve as the main access route to and from the mine for the transportation of materials, equipment, and concentrate. Truck transportation and the Diamond Point port would operate year-round.

The Alternative 3 road system would include 17 bridges that range in length from approximately 40 to 625 feet, and approximately 105 culverts - 37 of which would be designed for fish passage.

75 miles across Cook Inlet

The main compressor station for the line would be located on the east side at Whiskey Gulch.

Pebble Limited Partnership LLC drew a land use permit in April 2019 from the Alaska Department of Natural Resources State Pipeline Coordinator’s Section to cross state owned tidelands from the Whiskey Gulch access road off the Sterling highway, to conduct borehole drilling for geotechnical data collection.

The data is needed “to evaluate ground conditions for a proposed horizontal direction drill located near the point of origin of the proposed gas pipeline from the Kenai Peninsula.”

The total depth estimated for each borehole ranged from 120 feet to 300 feet, depending on geology encountered.

Two boreholes sites and work areas were designated; Site A is located along the Sterling Highway, and Site B is located along the beach at Whiskey Gulch. Site A access is directly from the southbound shoulder of the Sterling Highway.