Hilcorp’s plan to send divers to repair a damaged underwater gas pipeline — which is leaking between 210,000 and 310,000 cubic feet of methane a day into Cook Inlet — isn’t likely to happen until mid-to-late March, according to a Feb. 20 letter from Hilcorp Alaska Senior Vice President David Wilkins to the Alaska Department of Environmental Conservation’s Geoff Merrell, the On-Scene Coordinator for the leak.

The damaged pipeline was built in 1964 and until 2005 carried crude oil produced at off-shore platforms to land. It now carries processed natural gas — approximately 98 percent methane — to Hilcorp’s Platform A, which burns the gas as fuel and distributes it to three other Hilcorp platforms in the area — known as the Middle Ground Shoal — which are also gas powered.

Surface disturbances from the leak were spotted by a Hilcorp helicopter on Feb. 7 and reported to DEC that day. After ice covered the area, the disturbance was no longer visible. The ice has also inhibited Hilcorp’s plans to investigate and treat the leak with a team of divers, resulting in the expected delay.

DEC Coordinator Merrell first wrote to Wilkins regarding the leak in a Feb. 10 letter that requests five pieces of information from Hilcorp, including what alternatives the company has to the initial plan of responding with a dive team, and what plans Hilcorp has to monitor “potential impacts to resident or returning salmonid species, reproducing halibut populations, potential impacts to endangered species, and key prey species relied upon by these species.”

In his response, Wilkins summarized Hilcorp’s response actions up to that time: reducing platform activities to decrease the need for fuel gas, and dropping the pipeline flow to roughly 84 percent of its normal pressure. One shut-down operation, Wikins wrote, is the pumping of seawater to pressurize the Middle Ground Shoal’s oil-bearing rock. This water flood operation has been shut down on two of the four platforms — A and C — in the Middle Ground Shoal. Wilkins wrote that “over the course of time, the water flood shut down will impact the rate of oil production and may reduce the recoverable reserves from the field.”

As for alternatives to the dive plan, Wilkins wrote of three other repair options, all of which he stated would be less viable than repair by divers. Remote-operated underwater vehicles (ROV) aren’t available to Hilcorp, Wilkins wrote, adding that the silted water of Cook Inlet could blind a ROV’s cameras. Repairing the pipe by pushing extra tubing into it is impractical because the leak is the beyond the maximum reach to which tubing could be pushed, nor does technology exist to repair the leak from the surface without divers, he wrote.

Simply shutting down the pipeline and the platforms it powers could create worse problems, according to Hilcorp. The pipeline contains residual crude oil that could leak into the Inlet unless pressure is maintained in the pipe. With the platforms turned off, the parallel pipeline that presently brings crude oil to shore may freeze (due to the water content of crude oil) where it leaves the water, leading to an oil spill when it thaws in the spring, Wilkins wrote.

Because of these possible complications, Wilkins wrote that “it is not simply a matter of whether the methane leak continues until the Pipeline can be repaired.”

“Rather, the choice is between the current methane release … and one or more oil spills, along with other potential damage and additional risks,” Wilkins wrote.

Merrell will be responsible for evaluating the adequacy of Hilcorp’s response plans, according to Merrell’s letter to Wilkins.

“If your response actions are not satisfactory, (DEC) may assume the lead role in the investigation and cleanup efforts,” Merrell wrote to Wilkins, adding that Hilcorp may be held responsible for the cost of the state’s actions in this case. Hilcorp will also be responsible for the cost of the state’s oversight activities, Merrell wrote.

The possible environmental effects of the methane release remain uncertain. Wilkins cited Hilcorp-commissioned work by environmental consultant group SLR International, which estimated with a computer model that 84 percent of the leaked methane will reach the atmosphere,  while 17 percent is likely to be dissolved in the water, resulting in a water-methane concentration that Hilcorp’s study concluded would be 1/500th of the minimum methane concentration that DEC states will be harmful to marine life.

In a Feb. 24 letter to Director Chris Hoidal of the federal Pipeline Hazardous Materials Safety Administration regarding effects of the leak on harbor seals, belugas, porpoises, and other marine mammals, National Marine Fisheries Service Administrator James Balsiger wrote that “modeling efforts alone are not sufficient to reach a conclusion regarding potential effects to marine mammals” and recommended air and water sampling to determine effects. As of the letter’s date, no air or water samples had been made to determine methane concentrations at the site, Balsiger wrote. He cited other models that had shown potential for a zone of low-oxygen water surrounding the leak.

“Modeling suggests a relatively localized zone of low-oxygen, high-methane concentrations, but this has not been validated with incident-specific samples,” Balsiger wrote.

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