No venting at night? Agency finds tweaks to pipeline maintenance tools could reduce risks to residents




Turns out that making small changes to the operation of a natural gas pipeline maintenance portal — of which there are thousands in Pennsylvania — might significantly reduce the chances that nearby residents will be exposed to harmful levels of chemicals in plumes of gas.

A report by the Agency for Toxic Substances and Disease Registry, a federal health agency that modeled its research on a Washington County site, could bolster the case for installing similar controls — as Pennsylvania environmental regulators are proposing — to curb the release of gases from facilities known by the odd name of “pig launchers.”

The analysis found that cutting pressure in vented tanks and limiting releases to daytime hours at the pigging station along Fort Cherry Road in Mount Pleasant Township would nearly eliminate the risk.

That analysis was shared with the U.S. Environmental Protection Agency and the Pennsylvania Department of Environmental Protection this spring. Both the federal and state regulatory agencies are now focused on identifying other sites with high-pressure releases to make sure those facilities are also modified, an EPA spokesman said.

The company that operates the station said its sampling at the site proves that its emissions are well within safe levels.

The DEP’s goal is to cut down on releases of methane from natural gas well sites and infrastructure. To that end, it wants to require operations that release the most pollution to control 98 percent of the gases they would otherwise vent to the air.

A draft proposal also directs companies to follow the steps that the agency said slashed exposure risk in Mount Pleasant. That means routing high-pressure pig launcher chambers to low-pressure pipelines or vessels when available.

A DEP spokesman said about 2,800 pig launchers and receivers in the state reported emissions for 2015, the most recent reporting year. It is not clear how many have been modified because the pressure of each station is not reported into DEP systems.

Pig launchers?

Pig launchers and receivers look like pipelines that have arched above ground before dipping back into the earth.

They allow operators to send cylindrical cleaning or inspection tools called “pigs” through the pipeline and then catch them at another spot. Gas is often vented to moderate the pressure when pigs are loaded or removed.

The Agency for Toxic Substances ran the computer model because it was interested in exploring “potential immediate short-term exposures.” It used air sampling data collected at the Mount Pleasant station from the EPA coupled with simulated weather variations to identify conditions when residents in two homes within 300 yards might be at short-term risk.

EPA spokesman Roy Seneca said he could not say when or why the EPA collected the sampling data because the information “is part of an ongoing investigation.”

The model indicated that if gas from the pig launcher had been vented directly from a high-pressure tank during stable nighttime weather conditions, residents could have been exposed to methane at concentrations that could cause “potential irreversible health effects” when they were downwind.

After the equipment was modified to route gas to a low-pressure pipeline in July 2015, the model found that no meteorological conditions would have put either house in that threat zone.

Nighttime releases under certain conditions could have exposed both of the houses to benzene concentrations above a much lower threshold defined as “minimal risk.” If venting were kept only to daylight hours, potential exposures above even the minimal risk level could be nearly eliminated, the agency wrote.

The agency cautioned that the model was based on a series of assumptions, including that weather patterns at Pittsburgh International Airport in Findlay could be used as a proxy for meteorological conditions at the site 12 miles away.

Emissions were likely lower even than the modeled scenario for the low-pressure releases because the Mount Pleasant facility actually used a flare to burn off the gas rather than venting it straight to the atmosphere.


PG graphic: Pipeline pigging stations (Click image for larger version)

No public health concern

Past Agency for Toxic Substances reports from around the same site and a separate natural gas site in Chartiers Township based on samples taken at nearby homes found the levels of chemicals detected in the air were not expected to harm the health of the general population.

Those reports from 2015 and 2016 would have measured the impact from a greater assortment of natural gas-related infrastructure with collectively larger emissions, although the earlier sampling in Mount Pleasant was too limited for the agency to say conclusively whether breathing contaminants in the air there could harm residents.

The EPA also analyzed the sampling data from homes at the Chartiers site and concluded the monitoring there “did not indicate any level of concern.”

The past studies were based on different methods than the current analysis. The health agency’s Chartiers report noted the sampling there might not have captured “uncommon but significant incidents” when peak emissions coincide with unfavorable meteorological conditions and wind direction — just the kind of worst-case conditions the agency tried to model in the new analysis.

MarkWest Energy, which operates the pig launcher in Mount Pleasant, said its sampling at that station and 17 others found that even the maximum benzene concentrations it detected were well below the Agency for Toxic Substances’s minimal risk level.

It shared the data with state and federal regulators in November 2015.

“Actual data from this location and that of other locations in the area — including data generated as part of a review of launcher and receiver operations initiated by the U.S. EPA, as well as data from sites monitored in real time by [the Agency for Toxic Substances] — conclusively demonstrate that there is not a public health or environmental concern associated with these operations,” Robert McHale, MarkWest’s northeast environmental director, said in a statement.

He said MarkWest has also worked in consultation with state and federal regulators to make design enhancements at its pigging stations to further reduce its environmental footprint. 

Pushback on methane proposals

The natural gas industry and its supporters have pushed back against the DEP’s broad proposal for new methane permits, calling it a regulatory overreach that will add burdensome requirements with little environmental benefit.

The DEP collected company-reported air data from pigging stations as part of its 2015 shale gas emissions inventory, which it released late last month. Among the 10 categories of emissions sources, like drilling rigs and engines, pigging was the smallest source of volatile organic compounds emissions — a class that includes benzene — and the second-smallest source of methane emissions.

The agency’s pigging proposal came under particular scrutiny from state Senate Republican leaders earlier this year, who asked the DEP to explain “whether such a standard is even practical or attainable.”

DEP Secretary Patrick McDonnell defended the proposal in February, saying emissions from pigging operations originally had been considered of minor significance until it became clear from company reports that they had been “significantly understated by industry.”

Laura Legere: llegere@post-gazette.com.

 

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