Hilcorp plans to observe the methane release from its leaking Cook Inlet pipeline by using sensor buoys to make weekly water quality samples and twice-monthly air samples, and to monitor effects on wildlife with twice-weekly helicopter surveys covering an approximately five-mile radius of the leak.
In a Feb. 27 letter, the Alaska Department of Environmental Conservation required Hilcorp to submit a plan to monitor the leak’s environmental effects by March 8. On Tuesday DEC gave Hilcorp “general, preliminary initial approval to commence the sampling and monitoring plan” prepared for Hilcorp by consultants SLR International and subcontractor Kinnetic Laboratories. The plan’s specifics, though, “are still being evaluated by a host of government agencies and technical experts, and (DEC) may ask for modifications, clarification or operational changes in the future and/ or as a result of the sampling/ monitoring results,” DEC On Site Coordinator Geoff Merrell wrote.
The leak in a pipeline carrying natural gas fuel to four Hilcorp platforms in the Middle Ground Shoal area of Cook Inlet was discovered Feb. 7 and is believed, by Hilcorp, to have begun in December. As of Tuesday, the leak’s release rate is between 193,000 and 215,000 cubic feet of methane per day, according to a DEC report.
The DEC report also states that at least two overflights of the area near the leak have been done since March 8, neither of which spotted birds within 20 miles of the leak, though “hundreds of birds were seen on the western side of the inlet.”
Aboard one flight was an observer from International Bird Rescue, a bird conservation non-profit whose Response Services Director Barbara Callahan said migrating birds are unlikely to be in the area until mid-April. The birds that spend winter in Cook Inlet include scoter and eider sea ducks, she said, which are more likely to be in the open waters to the south than in the ice-bound upper Inlet.
As of Thursday, the National Weather Service’s Alaska Sea Ice Program shows that the area around the platform is nine-tenths ice-covered — a fact that is also delaying planned repairs of the pipeline by a dive team.
Callahan said the leak’s timing is fortunate, at least for the birds that are likely to be absent from the area.
“If I was going to pick a time of year for something like this to happen, this would probably be the best, except that it’s the ice that’s preventing them from fixing it,” Callahan said.
The DEC report also states that no belugas or marine mammals were seen on either flight.
Hilcorp plans to make fish and wildlife search flights twice a week, covering a 20 square mile circle above the leak.
Hilcorp’s response will follow two safety warnings that the Coast Guard and the Federal Aviation Administration have issued. On Feb. 15 the Coast Guard warned mariners to stay outside a 1000-yard radius of the leak’s surface disturbance, which “when not obscured by ice presence, is approximately 20 feet (ft) in diameter,” Hillcorp’s plan states.
The FAA also put a temporary flight restriction within one nautical mile of the leak site, authorizing only Hilcorp aircraft responding to the leak.
Callahan said the wildlife search flights will stay above 1000 feet of the leak, and Hilcorp’s plan keeps boats outside the 1000 yard distance for its air and water monitoring, though acoustic monitoring will come within 500 yards.
Sensor-buoys will be dropped up-current of the release area to float through and be collected on the other side. A line extending below the bouy will have sensors mounted at two, eight, and fifteen meters below the surface to measure concentrations at those depths of methane, oxygen and carbon dioxide.
The buoys will also deploy sampling bottles to collect water that will be analyzed by contractors ALS Environmental in a laboratory in Simi Valley, California.
Another type of buoy will be outfitted with sensors to measure oxygen, methane and carbon dioxide concentration in the air. Responders will deploy the air quality buoys twice a month, while spending one day each week on the water quality buoy monitoring, aiming to sample at every point in the tidal cycle by doing four or five drifts per day. Each drift is estimated to take one to two hours, with the buoys spending 20-60 minutes over the leak site.
“Therefore, if conditions are favorable, 2 to 3 deployments could occur over a given tidal stage (ebb or flood),” the plan states. Ice will be a factor here, too — the plan estimates a buoy destroyed by ice could result in a minimum three-week delay.
According to Hilcorp’s plan, the water-monitoring buoys are expected to be ready Friday and the air-monitoring buoys are expected to arrive on Monday.
Hilcorp will report to the agencies daily on ice conditions and the pipeline’s estimated leak rate and pressure, and also arrange overflights for Agency representatives every two weeks. It will report on sampling activities to DEC every Wednesday.
Human collection of air and water samples was among the possibilities considered in the plan but rejected “given the extreme flammability of (methane) and the inherent potential for an ignition source associated with equipment needed to access the site (whether boat or helicopter).”
Use of remote-operated underwater vehicles for water sampling was rejected because none are available and aerial drones were rejected as an air-sampling method because their rotors could spark an explosion.
Associate Professor of Oceanography Peter Winson of the University of Alaska’s College of Fisheries and Ocean Sciences said his department made suggestions for the sampling work and is presently helping them to acquire the necessary sensors and other equipment. He and two of his colleagues may come to the leak site to do measurements themselves, either before the leak is sealed or after.
“It’s interesting for us because the environment there is fairly challenging,” Winson said. “There are strong tidal currents and a high degree of sediments in the water column, and it’s a fairly significant amount of methane that’s leaking out. So with the tidal currents switching with the ebb and flow tides, it’s going to be an interesting challenge for us to do these measurements. We’re excited to figure that out and work with Hilcorp, and help the state of Alaska and the company make sense of what’s going on.”
Winson said he knows of studies of naturally-occurring methane seeps beneath ice in the arctic, “but that’s a very different saturation with a very different volume, flow and concentration.” He didn’t know of other situations resembling the Hilcorp leak, but said an opportunity to study it is “a scientific bonus in all this.”
“It could probably be a specific case study for future problems or natural leaks in this kind of environment that Cook Inlet presents,” he said.
A possible effect of the underwater leak is hypoxia — a situation in which methane displaces oxygen in the surrounding water, creating a deoxygenated state in which fish could asphyxiate.
The water’s oxygen content is of legal as well as environmental interest, the plan notes. Although there are no water quality standards for dissolved methane and carbon dioxide, state water quality standards set minimum limits for dissolved oxygen.
A Hilcorp-commissioned simulation predicts that hypoxia is unlikely to result from the leak. The computer model, performed by SLR International, calculated that 84 percent of the leaked methane will reach the atmosphere, while 17 percent is likely to be dissolved in the water, creating a water-methane concentration 1/500th of the minimum methane concentration that DEC previously identified as harmful to marine life.
One of the plan’s stated purposes is to “validate the modeling efforts being conducted by Hilcorp to estimate the concentrations of (methane) and dissolved oxygen in the vicinity of the release.” The cover letter Hilcorp submitted to DEC with its plan states that “sampling will supplement modeling” and that Hilcorp believes “the modeling provides a realistic picture of the potential impact of the release on water and air quality and expects the results from the sampling program described in the enclosed work plan to be consistent with the modeling results.”
National Oceanic and Atmospheric Administration Public Affairs Officer Julie Speegle said her agency has requested to see the raw data from Hilcorp’s monitoring, which NOAA would analyze to determine whether a hypoxic zone is being created, and if so, how large it is and to what degree oxygen is displaced from the water.
“This would enable us to characterize the impacted area and analyze the potential effects to Cook Inlet belugas and the physical and biological features that define designated critical habitat,” Speegle wrote in an email.
NOAA will also analyze acoustic data, which Hilcorp will gather by suspending recorders from floats, for the same purpose. NOAA has designated the area of Cook Inlet around the leaking pipe as critical habitat for endangered beluga whales.
The federal Pipeline and Hazardous Material Safety Administration, which regulates the safety of the pipeline, has given Hilcorp until May 1 to repair it or shut it down. Ice cover has delayed Hilcorp’s plans to have a team of divers repair the leak, and the company has previously estimated that repairs could be made by mid- to late March.
According to a three-month sea advisory issued Feb. 23 by the National Weather Service’s Alaska Sea Ice Program, the area where the pipeline is located — north of Cook Inlet’s forelands region — is expected to be less than three-tenths ice by the third week of April and ice-free by the fourth week of April.
Ben Boettger can be reached at firstname.lastname@example.org