The Alaska Department of Environmental Conservation is requiring Hilcorp Energy Company to begin sampling and environmental monitoring of its damaged underwater natural gas pipeline, which has been leaking between 210,000 and 310,000 cubic feet of methane gas per day into Cook Inlet since early February.

In a Feb. 27 letter to Hilcorp Alaska Senior Vice President David Wilkins, Geoff Merrell, the Alaska Department of Environmental Conservation’s on-scene coordinator for the leak, gives Hilcorp until March 8 to send his agency a plan to gather data on the environmental effect of the continuing leak.

Hilcorp plans to send a team of divers to repair the leak — spotted by a Hilcorp helicopter on Feb. 7 — though Wilkins previously wrote to Merrell that ice in the Inlet is likely to delay this repair until mid- to late March.

As of Feb. 24, no samples have been taken of the air or water affected by the leak, according to a letter with that date from from National Marine Fisheries Service Alaska Region Administrator James Balsiger to the federal Pipeline and Hazardous Materials Safety Administration.

Because “results of the sampling and monitoring program could necessitate an order to evacuate the line to control the release,” Merrell’s letter also requires Hilcorp to send DEC a plan by March 13 for how it would shut in its wells and deactivate the pipeline, if required to.

The leaking pipeline carries processed natural gas used as fuel by four Hilcorp platforms in the Middle Ground Shoal field, approximately 5 miles off-shore near Nikiski. Hilcorp representatives have previously said that turning off the leaking pipe — thereby cutting off power to the platforms — could release oil into the Inlet if the pipeline, which previously carried crude oil and may still have crude residue inside, floods.

In previous correspondence with DEC, Hilcorp cited a computer simulation of the leak and its environment to “demonstrate the relatively small impact that the release is likely to have on methane concentrations in the water column near the plume,” according to a Feb. 20 reply to Merrell by Wilkins.

The simulation, done for Hilcorp by environmental consulting group SLR International, concluded 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.

Though Merrell wrote that the simulation and other work Hilcorp cited is “helpful,” he stated that it does “not satisfy the need for real-time, on-site empirical data necessary to conduct an impact assessment and prove the veracity of the model.”

The requirements DEC gave Hilcorp include weekly observations for live or dead fish or birds, measurements of dissolved methane, oxygen, and carbon dioxide in the water near the leak, air quality measurements, and monitoring of the leak’s acoustic effects in the Inlet waters, with weekly reports of results to Merrell.

Merrell wrote that “…delay or insufficient work plan preparation or quality may result in Hilcorp being deemed an unresponsive responsible party,” in which case DEC would take over the leak response, with Hilcorp financially liable for their work.

The area of Cook Inlet around the leaking pipe is designated critical habitat for endangered beluga whales by the National Oceanic and Atmospheric Administration. According to NOAA’s Balsiger, the Cook Inlet beluga population is estimated to consist of 340 individuals.

“There is a need to understand the environmental impacts, no matter how minor, on the environment of Cook Inlet, and particularly to the food web supporting the beluga whales,” Merrell wrote.

In addition to the possibility of methane displacing oxygen in the water, underwater noise from the leak could be another impact. The acoustic effects could have “implications for Endangered Species Act-listed species and their prey since it could affect feeding and transiting patterns within and beyond this portion of their critical habitat,” Merrell wrote.

Though a Feb. 23 flyover in search of belugas didn’t spot any, according to a DEC statement released Wednesday, the area around the leak is within the belugas’ preferred winter foraging grounds, Balsiger wrote. Harbor porpoise populations also have “a high likelihood of overlap in time and space” with the gas leak. Other marine mammals that may be affected include stellar sea lions, dall porpoise, killer whales, and humpback whales, though these are less likely to be near the leak this time of year, according to Balsiger.

Two conservation groups have threatened legal action against Hilcorp for the leak under the federal Clean Water Act, which allows private parties to sue for violations with 60 day’s notice. Cook Inletkeeper announced its intent to sue Hilcorp on Feb. 15. On Feb. 27, the Arizona-based Center for Biological Diversity requested that Environmental Protection Agency Administrator Scott Pruitt also act against Hilcorp, and gave notice of its intent to sue Hilcorp if the EPA does not.

In response to an emailed request for comments, Hilcorp External Affairs Manager Lori Nelson wrote that the company plans to release a statement on Thursday.

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