By Steve Gorman
LOS ANGELES (Reuters) - The Southern California Gas Co would be required to install a system to siphon off and incinerate some of the methane spewing into the air from a subterranean pipeline rupture under a plan being weighed by local regulators to curtail the huge leak.
A five-member hearing board of the South Coast Air Quality Management District was due to review and possibly vote on the proposal at a public meeting Saturday in Los Angeles, near the site of the leaking underground natural gas storage field.
The stench of gas fumes has sickened scores of nearby residents and led to temporary relocation of at least 2,850 households from the Porter Ranch community at the edge of the Aliso Canyon facility since the leak was detected on Oct. 23.
SoCal Gas, one of the nation's biggest gas utilities and a division of San Diego-based Sempra Energy, has said the leak was caused by a broken injection-well pipe several hundred feet beneath the surface of the 3,600-acre field.
The company normally pumps surplus supplies of natural gas into vast underground reservoirs beneath the site in summer when energy demand is low, and draws on that excess inventory in winter as demand rises.
Methane, the principal component of natural gas and a far more potent greenhouse gas than carbon dioxide, has been seeping out of the ground in amounts never before seen in California.
At one point the California Air Resources Board estimated gas was escaping at the rate of 58 tonnes per hour, accounting for roughly one-fourth of all methane emissions throughout the state.
Several attempts by the company to halt the leak have failed. But the flow has diminished as the utility began withdrawing gas from the field at twice the normal rate to ease underground pressure, company spokeswoman Melissa Bailey said.
In the meantime, the Air Quality Management District plan calls for installation of special equipment to capture a portion of the leaking gas from the wellhead and burn it off at extremely high temperatures.
Bailey said company was already designing such a system, but district spokesman Sam Atwood said, "They're doing it with the full knowledge that they're going to be required to do it."
The district's proposal also would require SoCal Gas to withdraw as much of the remaining gas underground as quickly as possible while maintaining reliable supplies for customers.
The company said in early December it would take at least three more months to plug the leak by drilling a relief well to intersect the damaged pipe and inject it with fluids and cement.
The district's proposal also calls for deodorizing the escaping gas, more air quality monitoring, additional reporting to regulators and a study of health effects.
(Reporting by Steve Gorman; Editing by Lisa Shumaker)