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Emissions, Storage Pressure Eyed in Fed, State Probes of Aliso Canyon

Separate federal and state probes are now underway in California as the Aliso Canyon underground natural gas storage well leak continues to draw the spotlight. The leaking well in the foothills northwest of downtown Los Angeles has officials focusing on unanswered questions regarding the volumes of methane escaping into the atmosphere and the extent to which over-pressurization led to the well failure.

Southern California Gas Co. (SoCalGas) officials have maintained from the start that no accurate assessment of the volumes emitted can be made until after the well is plugged and sealed, and state regulators concur. However, some state government officials are making regular weekly estimates of the possible volumes of methane escaping. The readings vary greatly and are strongly couched as "very preliminary" by the California Air Resources Board (CARB).

At the urging of U.S. Rep. Brad Sherman (D-CA), the U.S. Environmental Protection Agency (EPA) has opened an investigation. State Assemblyman Mike Gatto from the San Fernando Valley, who chairs the utilities and commerce committee, said he will hold hearings in January on the incident, which has caused the relocation of several thousand residents who live near the facility.

EPA issued a mandatory information request for responses from SoCalGas by Thursday, seeking assurances that operations at Aliso Canyon have not violated the federal Clean Air Act.

On Tuesday, SoCalGas officials acknowledged that for the past two weeks, in consultation with the California Public Utilities Commission (CPUC), the Sempra Energy gas utility accelerated withdrawals from the 86 Bcf capacity storage field to reduce pressure in the leaking well. As a result, the storage field's capacity has fallen from 93% to 58%.

Regarding the pressures in the field, SoCalGas distinguishes between storage field pressures and the overall abandoned oilfield pressures and operates "pipelines and facilities in accordance with state regulatory codes," a spokesperson told NGI on Monday.

He reiterated that the company and regulators don't know the cause of the leak but after it has been stopped they will address that question. "We conduct weekly checks of pressure readings to confirm each well's condition. Any unexpected finding from these tests leads to further analysis and work designed to make sure the concern is addressed. In the weeks prior to Oct. 23 when the gas leak was discovered, we did not receive any pressure readings that would cause concern."

He said there is no maximum allowable operating pressure (MAOP) for the facility, as there is for major natural gas transmission pipelines. There is, however, a MAOP for the field pressure.

California has aggressive greenhouse gas (GHG) emissions reduction goals (see Daily GPIApril 30), and the Obama administration has called for nationwide reductions (see Daily GPIAug. 17March 28). The pressure to calculate the facility leak's emissions and to plug it has grown.

As of Dec. 23, CARB showed potentially substantial cumulative emissions of methane, but the leakage rate has been cut in half over the past four weeks. "The leak rate is expected to vary as attempts are made to stop the leak and as gas is withdrawn from the reservoir," according to CARB's Aliso Canyon report published online. "Continuous measurements are also being collected as part of the state's GHG monitoring network and through other complementary measurement efforts."

On Dec. 22, the leak rate had dropped to 30,300 kilograms of methane/hour (kgm/h) from 58,000 kgm/h at the end of November. "You could say [the leak rate] has been halved, but you really should include the point that there has been a fairly wide margin for error included simply because at this point we don't know how variable the flow is," a CARB spokesperson told NGI.

The cumulative total for the GHG carbon dioxide equivalent of methane was estimated on Dec. 22 to be 1.6 million metric tons (mmt), up from 1.5 mmt 10 days earlier.

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