Every Hour, This Gas Storage Station Sends Half a Ton of Methane Into the Atmosphere

PETAL, Miss.—The Petal Gas Storage Station lies halfway between the winding banks of the Leaf River and the International Checker Hall of Fame. It’s a warren of pipes, wellheads and metal buildings where noisy compressors pump gas underground and then suck it back up to the surface again. 

In the process, the Petal plant releases half a ton of a potent greenhouse gas into the atmosphere every hour—more than any other gas storage facility in the country.

Petal is just one of the many underground natural gas storage facilities in the United States. They pump gas into underground salt formations and depleted oil and gas reservoirs.

The Petal plant is hidden beneath a huge dome of salt that measures nearly two miles in circumference. It formed millions of years ago during the Mesozoic Era when other layers of rock pushed down upon the surrounding salt formation until it was compressed upwards into a bulging dome.

A gas company began hollowing out the Petal Dome, creating the nation’s first salt cavity specifically designed for natural gas storage in 1951. Today, eight artificial caverns carved into the Petal Dome store up to 30 billion cubic feet of natural gas, fuel that provides a critical backstop for the region’s fluctuating energy needs.   

The Petal storage facility is small compared to gas storage facilities. It ranks as the 41st.^stLargest underground gas storage facility. Its methane emissions are among the highest of all such facilities.

In 2020, Petal emitted 4,947 metric tons of methane, according to reports submitted by the facility’s owner, Gulf South Pipeline, and its parent company, Boardwalk Pipeline Partners, to the U.S. Environmental Protection Agency. The methane released from Petal was three-and-a half times greater than any other U.S. gas storage facility.

According to data provided by the companies to the EPA, the Petal facility holds the dubious distinction for being the largest methane emitter in the country for the past five years. Boardwalk and its subsidiaries owned three of the seven largest gas storage facilities that emit the most methane in 2020. 

Gulf South and Boardwalk have begun to curb emissions at the Petal facility, cutting them in 2020 by nearly 50 percent of what they were in 2019, a year when Petal’s emissions were more than five times larger than any other underground gas storage facility in the country. Boardwalk executives stated that they have cut emissions by 54 percent again in 2021.  

The EPA has not yet verified Petal’s 2021 emissions. If they are correct, Petal would still be a major methane emitter among gas storage units in the country, compared to the most recent available data for all of them. 

These emissions are particularly concerning because methane, an extremely potent greenhouse gas, has a direct impact on climate change. Over a 20-year time period, methane is 81x more potent at warming the climate than carbon dioxide.  

Over a period of 20 years, emissions from Petal’s storage station equal the annual greenhouse gases emissions of 87,000 cars, more than Petal and Hattiesburg combined.

The Petal facility’s emissions do not violate any state or federal laws, but they call into question the ability of the oil and gas industry to voluntarily curb its own climate pollution.  

About 25% of methane emissions in the natural gas industry comes from transmission and storage sectors.  The EPA has proposed a rule that would reduce methane emissions for existing gas storage and transmission facilities.

A Federal Energy Regulatory Commission environmental assessment was done for the expansion of one Petal compressor station. This 2019 report found that methane does not pose a danger to human health and that the compressors do not lie within 1,000 feet from any residences. 

In July 2021, leading health organizations such as the American Lung Association, American Academy of Pediatrics and Physicians for Social Responsibility wrote to Michael Regan, urging him to take more severe measures to reduce methane gas emissions from oil and natural gas operations. 

“Extraction, processing, transport and distribution of methane all contribute to emissions, both of methane and of accompanying pollution like volatile organic compounds (VOCs) and toxic gases,” the letter said. “These emissions pose serious threats to human health, directly as in the case of exposure to toxic gases as well as the smog formed from VOCs, and due to methane’s contribution to climate change.”

Many leaders from Mississippi’s Black Church wrote to Regan in support for the proposed regulation in January after the EPA published a proposed rule change that would impose more stringent standards. They pointed out that their communities are greatly affected by natural gas facilities. They called the proposed regulation an “important step forward.” 

Gerald Steele, an alderman in Petal whose ward includes the gas storage site, expressed surprise that the Petal plant’s emissions were the highest from such facilities in the nation. He stated that the company was a major financial contributor to the area through its employment and tax contributions. But the news about the emissions, he said, was “really alarming.”

The EPA has been a partner with oil and natural gas companies through the Natural Gas STAR program. It helps them reduce their emissions. A 2006 industry and EPA report showed that Petal could reduce compressor emissions by over 90 percent. The capital costs for such fixes were so low—several thousand dollars per compressor—that operators could recoup their costs in as little as a month through reductions in the loss of valuable natural gas. 

Boardwalk did no respond to an inquiry regarding the Gas STAR Report. Although the company has made progress in reducing its emissions, EPA documents show that they have not followed the recommendations of the report as of 2020.

Simple economics make the facility’s outsized emissions perplexing: Natural gas released from the Petal storage facility had a wholesale value of approximately $500,000 in 2020. This would appear to be a loss in revenue annually for Boardwalk or its customers.  

Boardwalk is a gas transportation and storage provider. Gulf South is also a service provider. They don’t buy and sell natural gas, but store it and transport it for others, an arrangement that could reduce some of Boardwalk’s incentive to fix leaks.   

“My guess is Boardwalk Pipeline [Partners] does have financial incentives to prevent leakage because they would be liable for losing their customers’ gas, although contracts often include a permitted amount of gas lost in transportation and storage,” David Lyon, a senior scientist with the Environmental Defense Fund, said.  

Boardwalk said Gulf South’s terms for lost gas can be found in a gas tariff document held by the Federal Energy Regulatory Commission. However, as this article went to press, it wasn’t immediately clear which document they were referring to.   

Lyon spends his days researching technologies and policies to reduce natural gas industry leakages and looking at emissions data. He seems baffled as to why Boardwalk wouldn’t have implemented such cost-effective fixes many years ago. 

“It doesn’t make sense,” he said.

Director of the Colorado State University’s Methane Emissions Technology Evaluation Center, Daniel Zimmerle is an expert in quantifying and finding ways that to reduce the emissions from similar oil and gas operations to the Petal facility. But he, too, said he had no explanation for the facility’s high methane emissions.  

“It just seems really unusual,” Zimmerle said.

Emissions from Leaky Valves

The reason that Petal’s outsized methane emissions have persisted for so long—more than a decade after other gas companies and the EPA showed how they could be all but eliminated—might remain a mystery, but the source of the emissions is well-documented. 

Geology is not to blame. Underground storage is very effective at trapping natural gasoline under layers of impermeable stone that prevent it from escaping, regardless if salt caverns and other rock formations were used. A recent study revealed that the average daily methane concentration in soil near underground storage wells was 0.1% per day. This is less than what a cow would urinate over a 24-hour period. 

However, at Petal, “reciprocating compressors,” which use pistons to pressurize natural gas  for storage or to push gas through the regional pipeline network, were responsible for 99 percent of the 4,947 metric tons of methane that the facility released in 2020.

The vast majority of these emissions came from the compressors’ “isolation valves,” which disconnect the compressor from both the underground storage and the regional gas network when the compressor is not in use.

If natural gas is not being delivered to a region in peak demand times, compressors can be left idle for large portions of the year. This is the case with the Petal storage station, where the facility’s compressors sat idle for nine months on average in 2020. 

But Petal’s isolation valves are leaky. Instead of shutting off gas completely when closed, the isolation valves allow thousands of tons of methane to pass into the facility’s idled compressors. Once inside the compressors, the gas escapes into the atmosphere through open “blowdown valves.”  

When Inside Climate News first inquired about the emissions from Petal in June 2021, Boardwalk Pipeline executives said the facility’s outsized emissions were a reflection of the site’s size and the role it played in the regional gas network. The Petal gas storage facility used a larger than usual number of compressors, not only to pump gas in and out of storage but also to push gas through the company’s transmission pipelines, they said.     

“When the total emissions reported for this facility are broken out on a per compressor unit basis, they are comparable with other companies listed on the same EPA report,” Jillian Kirkconnell, a spokeswoman for Boardwalk Pipeline Partners said in a written statement.

But an analysis of emissions data from Petal by Inside Climate News found that the gas storage facility’s emissions in 2019 and 2020 were more than three times higher on a per compressor basis than the emissions rate from individual compressors averaged across each of the nation’s top 10 methane-emitting, underground gas storage facilities. 

In fact, methane emissions from just one compressor at the Petal Gas Storage facility emitted more methane in 2020—2,355 metric tons—than the total methane emissions from any other gas storage facility in the United States that year. 

Zimmerle stated that releases of such magnitude can cause frost to form around the equipment that leaks as the pressurized gases escapes.

“You should see that if you’re at the site,” he said of the frost. “It should be pretty obvious to them.”

Zimmerle stated that he initially doubted the amount of emissions from the Petal facility. He also noted that some individuals who take measurements and report data on any site can accidentally add a zero, inflating the emissions. Zimmerle stated that he changed his mind after seeing how the company’s emissions had increased year after year. He also acknowledged the efforts it is making to reduce them. 

Boardwalk Pipelines did indeed not dispute the 2020 data they submitted to the EPA. In fact, the company highlighted compressor emission in its sustainability report published last years. 

The company did not dispute the Inside Climate News analysis that concluded that the Petal facility’s emissions are significantly higher per-compressor than similar gas storage sites.  

The company did however note the 2021 reduction in methane emissions from the Petal gas storage area and that it reported these reductions the EPA. Taylor Gillespie, a spokesperson for the EPA, stated that the agency is still verifying the emissions from 2021 that Boardwalk submitted earlier this year and could not verify the reductions.  

Even if Boardwalk reduced emissions at the Petal facility as much as they claimed from 2020 to 2021, the plant’s methane emissions would still be 60 percent higher than any other underground gas storage site in the country, when compared to the most current emissions data available for other facilities. 

A ‘Workable Solution’ Ignored

In the company’s first sustainability report, released last year, Boardwalk noted that it is modifying and replacing older compressor equipment to reduce methane emissions.

“Boardwalk is continuing to take steps to reduce emissions across its systems and compressor stations,” Kirkconnell said.

She added, “a number of compressor blowdown valves and isolation valves have been repaired or replaced and procedures at the facility have been modified to minimize methane losses when units are not in operation. This resulted in significant reductions in methane emissions from 2019 to 2020 to 2021.” 

Climate advocates say the reductions are welcome news, but they add that it’s unclear why it took the company so long for those emissions reductions to begin.

The 2006 Gas STAR report emphasized as a “prudent operating practice” that operators should keep compressors pressurized when they are not in use, something the report states will reduce emissions by as much as 68 percent, at no cost, by eliminating isolation valve leaks. In addition, maintaining low gas pressure in idle compressors can pose additional safety risks inside compressor buildings. However, it also discussed precautions you could take to mitigate any additional risk.

“There is no reason to believe it is not a workable solution,” said Zimmerle, of Colorado State University.   

Zimmerle stated that there are many strategies compressor operators can use to reduce their emissions. Gas company National Fuel reported recently a 95 to 99 percent reduction in emissions on two of its compressors, simply by replacing the leaky isolation valves.   

Still, nearly two decades after the EPA-industry partnership’s report detailing its emission reduction strategies, Boardwalk and most other gas storage operators continue to depressurize their compressors, and report high emissions, when their compressors are not in use.   

“It’s been over a decade since EPA published this report and there are still these significant emissions,” Lyons, the Environmental Defense Fund scientist, said.  

A Proposed Rule might make a difference

Boardwalk indicated in its most recent annual report to the U.S Securities and Exchange Commission that failing to reduce its carbon emissions could pose a threat to its business.

“Increased attention to climate change, environmental, social and governance (ESG) matters and conservation measures may adversely impact our business,” the company wrote in the report. “Companies that do not adapt to or comply with investor or other stakeholder expectations and standards, which are evolving, or that are perceived to have not responded appropriately to the growing concern regarding ESG issues, regardless of whether there is a legal requirement to do so, may suffer from reputational damage and other adverse consequences.”

Boardwalk also noted that its emissions might soon be regulated under the EPA’s proposed rule to establish standards of performance for methane emissions from new and existing sources within the oil and gas sector, including gas transmission and storage. The agency is expected to issue a supplemental proposal containing proposed regulations “later this summer,” Joseph Goffman, the EPA’s principal deputy assistant administrator for the Office of Air and Radiation, said during a confirmation hearing last month. The agency anticipates that the rule will be finalized by the end 2022.  

“The proposed rule includes several requirements relevant to our operations, including stricter emissions limits for various facilities and equipment (including pneumatic controllers, storage tanks, reciprocating compressors, and wet seal centrifugal compressors), more frequent leak detection and monitoring of fugitive emissions from compressor stations, and deadlines for repairing fugitive emissions,” Boardwalk’s financial report stated.

Lyon, of the Environmental Defense Fund,  said the rule will result in the reduction of  methane emissions by an estimated 60,000 metric tons from reciprocating compressors—the same type of piston-driven compressors used at Petal facility—at gas storage facilities alone. When measuring the climate impact over a 20-year period, that’s equivalent to taking just over 1 million automobiles off the road.  

Boardwalk noted in its sustainability report that it is an “active” member of the ONE Future Coalition, a group of natural gas companies working to voluntarily lower methane emissions across the natural gas supply chain. The group’s goal is to reduce methane emissions across the entire sector—from the wellheads of gas fields to the homes and businesses of end users—to less than 1 percent of total natural gas produced by 2025.

Boardwalk will have make significant additional cuts to align with this goal. Gas storage is a small subset of the gas industry and should make up a small fraction of the industry’s total emissions.  However, in 2020 Petal alone leaked approximately 0.6 percent of the natural gas it stored that year—a rate equal to 60 percent of the entire industry’s targeted emissions budget—based on the emissions and storage data Boardwalk reported to EPA.  

As You Sow, a non profit shareholder advocacy organization, has Danielle Fugere as its president and chief counsel. She said that although the Boardwalk’s recent actions are encouraging, they still have a long way ahead.

“You have to reduce your emissions to at least the level of other similarly situated companies, and even those companies need to do much more,” she said. “The first thing we would ask Boardwalk to do is to solve its compressor problems immediately, and then continue its work to reduce emissions year on year.”

This story was created in partnership with Mississippi TodayAlex Rozier, a Jackson, Miss.-based environment reporter and data analyst, is located at