March 8 (Reuters) - Last October, an Idaho farmer using

a backhoe punched a hole into a 22-inch (56-cm) pipeline buried

under a field, sending more than 51 million cubic feet of

natural gas hissing into the air.

While the incident on Williams Companies' ( WMB ) Northwest

Pipeline was big, it was no anomaly along the roughly 3 million

miles (4.8 million km) of natural gas pipelines crisscrossing

the U.S.

Accidental pipeline leaks - caused by things like punctures,

corrosion, severe weather and faulty equipment - happen

routinely and are a climate menace that is not currently counted

in the official U.S. tally of greenhouse gas emissions,

according to a Reuters examination of public data and regulatory

documents.

Pipeline mishaps unintentionally released nearly 9.7 billion

cubic feet of gas into the atmosphere between 2019 and late

2023, according to a Reuters examination of incident report data

maintained by the U.S. Pipeline and Hazardous Materials Safety

Administration (PHMSA).

That is the climate equivalent of running four average-sized

coal-fired power plants for a year, according to an

Environmental Defense Fund (EDF) online calculator.

Those emissions are currently not included in the nation's

official greenhouse gas count because federal rules exempt

large, unexpected leaks, and mainly only capture emissions from

regular operations, according to the U.S. Environmental

Protection Agency (EPA).

The Biden administration aims to change that as early as

next year under a set of rules proposed by the EPA to crack down

on methane emissions from the oil and gas sector, and which

would punish emitters with fees of $900 to $1,500 per metric ton

when they exceed a certain threshold.

Reuters relied on PHMSA data and interviews with

researchers, company officials and regulators to provide new

detail on the scale of greenhouse gas emissions from accidental

pipeline leaks that could soon be added to the official

greenhouse gas tally, as well as the potential cost to companies

under the looming fees.

"I don't think the public or regulators have realized just

how much methane has been lost from pipeline infrastructure,"

said Kenneth Clarkson, a spokesperson for the Pipeline Safety

Trust, a non-profit watchdog. "Newer studies have come closer to

capturing the true amount of emissions and this has started

catching the attention of policymakers."

Accidental leaks reported from PHMSA by the five biggest

U.S. pipelines between 2018 and 2022 showed that those incidents

could have significantly increased the facilities' overall

reported emissions, potentially resulting in fees of up to $40

million under the proposal.

The operators of the five biggest pipelines include

Berkshire Hathaway ( BRK/A ), TC Energy ( TRP ) and Kinder

Morgan ( KMI ).

Berkshire Hathaway's ( BRK/A ) 14,000-mile Northern Natural Gas

pipeline, for instance, reported unintended releases of natural

gas to PHMSA during the five year period that were the

equivalent of about 30% of the methane the facility reported to

EPA during the period.

Williams, the owner of the pipeline that leaked in Idaho in

October, reported unintended gas releases that amounted to about

15% of the methane it reported to EPA.

Berkshire Hathaway ( BRK/A ) and Williams did not respond to requests

for comment on Reuters' analysis or the EPA proposal.

TC Energy ( TRP ) said reducing its methane emissions was a critical

part of its business, but did not comment directly on the EPA

proposal or Reuters' analysis.

Kinder Morgan ( KMI ) said it does not exclude unintended emissions

from its reports to EPA, even though it is not required to

include them.

BIG DISCREPANCY

The Biden administration unveiled its batch of final rules

aimed at cracking down on U.S. oil and gas industry releases of

methane at the United Nations COP28 climate change conference in

Dubai in December, part of international efforts to curb

releases of the gas.

Piped natural gas is typically around 90% methane, a

greenhouse gas which is several times more potent in warming the

planet than carbon dioxide during the relatively short time it

remains in the atmosphere.

The new policies would ban routine flaring of natural gas

produced by newly drilled oil wells, require oil companies to

monitor for leaks from well sites and compressor stations and

establishes a program to use third party remote sensing to

detect large methane releases.

The new reporting requirements for large leaks, meanwhile,

are likely to be finalized later this year and take effect in

2025, the EPA told Reuters.

Under the proposal, companies will be required to report

abnormal leaks of about 500,000 cubic feet of pipeline gas or

more starting next year, a threshold significantly lower than

what PHMSA requires.

The new reporting rules would also apply to big, unplanned

emissions from other parts of the oil and gas industry, such as

drilling operations, EPA said.

The fact that some large methane leaks have never been

accounted for in U.S. greenhouse gas inventories underscore

concerns among environmental groups and scientific researchers

that emissions from the fossil fuel sector have been vastly

understated.

An Environmental Defense Fund analysis last year, for

instance, estimated U.S. pipelines leak between 1.2 million and

2.6 million tons of methane per year, or 3.75 to 8 times more

than EPA estimates.

The EDF figure includes not just large mishaps but also

pervasive smaller leaks on tiny distribution lines.

"The failure of EPA to account for these large events is a

big driver of that discrepancy," Edwin LaMair, an EDF attorney

who focuses on oil and gas regulations, said in an interview.

The Interstate Natural Gas Association of America, a

pipeline industry trade group, said most incidents reported to

PHMSA relate to safety systems operating as intended.

The group also pointed to an EPA analysis showing that most

transmission and storage facilities may not meet the 25,000

metric tons of carbon dioxide equivalent per year emissions

threshold required to pay the methane fee.

The EPA analysis said, however, that it was not yet possible

to accurately estimate "the magnitude of emissions that will be

reported and which facilities will report those emissions."

The pipeline industry has also said in public comments to

the EPA about the new reporting rules that they could lead to

double-counting of some emissions.