Last weekend contracted dive crews from Homer visited Hilcorp’s underwater fuel gas pipeline in Cook Inlet’s Middle Ground Shoal area and located the source of the rupture believed to have been leaking methane since late December. The danger presented by the Inlet’s iced-over surface had previously prevented divers from reaching the pipe.

According to a Monday announcement by Hilcorp, the leak — which initially released between 225,000 and 325,000 cubic feet of methane per day into the Inlet, but was greatly reduced after Hilcorp shut down the two oil platforms powered by the piped gas on March 25 — comes from a two-inch opening on the bottom of the pipeline, which divers found resting on a seafloor boulder.

The 8 inch diameter pipeline , built by Shell Oil Company in 1964, has leaked at least twice before in similar circumstances. Federal regulators of the Pipeline and Hazardous Materials Safety Administration cited leaks in August and June 2014, when the pipeline was owned by XTO Energy. According to PHMSA’s March 3 safety notice to Hilcorp, those leaks “were caused by rocks contacting the pipeline in areas where the pipeline was not continuously supported by the seabed.”

“The rocks contacting the pipeline deteriorated the steel pipe wall by abrasion, resulting from relative movement between the pipeline and rocks contacting the pipeline,” the PHMSA notice states. Both previous leaks were approximately two-thirds of a mile from the present leak and 42 yards apart from one another.

According to the Hilcorp announcement, divers are preparing the site for the installation of a temporary clamp around the pipeline. The pipeline has been leaking between 88,000-110,000 cubic feet of methane per day since Hilcorp’s March 25 decision to reduce the pipeline pressure to the minimum necessary to prevent it from flooding and to power the platforms’ safety equipment.

“Following completion of the initial repair, further inspection and work will be done to permanently repair the affected segment of pipe,” Hilcorp’s announcement reads. “The line will not be returned to service until permanent repairs have been completed, the line has been pressure tested, and regulators have approved a re-start.”

Anna Platform pipeline pressure-tested

Hilcorp’s Anna Platform, which was shut down April 1 after its crew felt an impact and saw bubbles from around one of legs, is still being investigated as a possible source of oil sheens that Hilcorp helicopters spotted in the Inlet later that day, the largest 10 feet by 12 feet.

The crude oil pipeline that carries Anna Platform’s production to the nearby Bruce Platform, from which a separate pipeline carries it to the onshore Granite Point tank farm, was the suspected source of the sheen. After the pipeline was cleaned and flooded the next day, a response team with officials from Hilcorp, Alaska Department of Environmental Conservation (DEC), and the U.S Coast Guard disbanded.

On Monday the Anna Platform’s pipeline underwent a pressure test that DEC spokesperson Candice Bressler wrote effectively ruled out the pipeline as the source of the oil discharge. According to a Hilcorp announcement, the 8-hour test put the pipeline at 125 percent of its maximum operating pressure, with the result that “the pipeline held pressure throughout the test, meaning the pipeline is in good working order.”

Other sources of the oil discharge — which DEC estimated at a maximum of 10 gallons, and Hilcorp estimated at less than 3 gallons, based on the size of the sheens observed and the amount of oil recovered from the pipeline — are still being investigated. DEC has required Hilcorp to submit a repair plan once the source is discovered.

The two leaks — as well Hilcorp’s emptying on April 3 of a suspected third leaking gasline from its Steelhead Platform — have prompted environmentalist groups to call for an inspection of Cook Inlet’s pipeline and platform infrastructure, much of which has survived from the 1960s amid the Inlet’s scouring silt and strong tides. The Arizona-based Center for Biological Diversity has petitioned PHMSA and DEC for such an inspection, as has Cook Inletkeeper in a letter to Alaska Governor Bill Walker.

Reach Ben Boettger at benjamin.boettger@peninsulaclarion.com.