PA Environment Digest Blog: DEP Issues Air Quality Operating Permit Authorizing The Expansion Of MarkWest Harmon Creek Natural Gas Processing Plant In Washington County

The Department of Environmental Protection published notice in the May 30 PA Bulletin announcing it issued a State Only Air Quality Operating Permit on May 18, 2026 authorizing the expansion of the MarkWest Liberty Midstream & Resources, LLC Harmon Creek Natural Gas Processing Plant in Smith Township, Washington County. (PA Bulletin, page 3212)

The permit would authorize the operation of air contamination sources and air cleaning devices associated with expansion of the plant to add a third cryogenic plant and a second de-ethanization plant.

Natural gas cryogenic plants take natural gas and cool it to sub-zero temperatures-- minus 120 degrees Fahrenheit-- in order to condense and separate out liquids like butane, ethane and propane from the gas.

These natural gas liquids are then shipped via pipeline to places like the Shell Petrochemical Plant in Beaver County to make plastics and through the Mariner East Pipelines to Southeast Pennsylvania as feedstock for other petrochemical plants and export.

Community Opposition

Residents living around the MarkWest Harmon Creek Plant urged DEP to deny a new Air Quality Permit for the facility based in-part on ongoing and frequent black smoke violations from the plant flare. Read more here.

Residents documented-- through cameras and visual observation-- 43 black smoke violations at the plant flare between October 26, 2025 to February 28, 2026-- an average of one violation every three days over four months. [List in Appendix A of comments.]

Black smoke indicates incomplete combustion of the natural gas and other chemicals going through the flare for safe destruction and is a violation of the facility’s existing air quality permit.

The comments said, “Despite this ongoing noncompliance, which has been reported to DEP, MarkWest has not self-reported any of these incidents that occurred on more than 40 separate days and we are not aware of any action MarkWest has taken to address the root cause of the ongoing visible emissions.”

“Given this ongoing noncompliance, Mark West has clearly demonstrated that they are “likely to cause air pollution or to violate the act, the Clean Air Act or the regulations thereunder applicable to the source” at Harmon Creek Gas Plant, which is grounds for DEP’s denial of this SOOP application under DEP’s regulations.”

“DEP must not, and may not, reward this noncompliant behavior with an operating permit unless and until it can demonstrate consistent compliance with air pollution laws, regulations, and permits.

“Granting the SOOP without such a demonstration would condone ignoring the law and unjustifiably endanger public health.”

Major Flare Event April 20-21

The natural gas/chemical 'emergency' flare at the MarkWest Harmon Creek Plant created a new sun in the sky at 4:47 a.m. on Monday, April 20 and again at 4:29 a.m. on Tuesday, April 21 shining in the windows of neighbors around the plant.

The flare event and continuing flare activity were captured on video by the Breathe Project cameras trained on the facility 24-hours a day.

The community was told the ‘emergency’ flare isn’t supposed to be used but a couple times a year, but the Breathe Project cameras capture evidence of the flare burning most nights and during the daytime.

Explosion/Fire

Residents are concerned about how natural gas processing plants are operated because on December 25, 2022, Energy Transfer’s Revolution Natural Gas Cryogenic Processing Plant right next to the MarkWest Harmon Creek Plant in Smith Township, Washington County, suffered a major explosion and fire that resulted in a nine and a half hour uncontrolled release of ethane and other vapors.

The fire burned for 11 hours, according to reports in the Observer-Reporter newspaper.

There has not been a publicly available report on what caused the explosion or how a similar incident could be prevented in the future.

Click Here for more background.

DEP just announced a June 25 hearing on an Air Quality Permit for the Revolution Natural Gas Plant covering an expansion of that facility. Read more here.

Final Permit, Comment Response Document

The final permit and a comment/response document responding to comments received on the MarkWest Harmon Creek Natural Gas Plant permit by DEP should be available for public review.

Documents like this are published on the DEP Southwest Regional Office MarkWest Harmon Creek Gas Plant webpage.

The DEP PA Bulletin notice said questions about the permit should be directed to Thomas Joseph, P.E., Environmental Engineering Manager, at 412-442-4336 or by email to: joseph@pa.gov.

Parties aggrieved by this action have 30 days from this notice to appeal the decision to the Environmental Hearing Board.

(Photo: Harmon Creek Natural Gas Plant ‘emergency’ flare event on April 20-21, 2026 captured by the Breathe Project cameras.)

Resource Links - Harmon Creek Plant:

-- Residents Around MarkWest Harmon Creek Natural Gas Cryogenic Processing Plant In Washington County Urge DEP To Deny A New Air Quality Permit After Ongoing Black Smoke Violations [PaEN]

-- The Sun Also Rises In Washington County: MarkWest Harmon Creek Cryogenic Natural Gas Processing Plant Creates New Sun - At 4:47 a.m April 20, Again On April 21 - And It’s Still Burning [PaEN]

Articles About The Air Permit Considered In 2025:

-- Washington County Resident To DEP: Harmon Creek Natural Gas Plant Expansion Will Result In A Huge Increase In Air Pollution, It Should Be Required To Have A Major Air Quality Permit, It Is Not A ‘Minor’ Source [PaEN]

-- Community Speaks Out Against Expansion Of Harmon Creek Natural Gas Processing Plant In Washington County [PaEN]

-- Moms Clean Air Force To DEP: Families In Washington County Are Already Living In The Middle Of Major Natural Gas Industrial Sites - Do Not Expand The Harmon Creek Natural Gas Processing Plant And Make It Worse [PaEN]

-- Center For Coalfield Justice To DEP: Harmon Natural Gas Processing Plant Should Be Required To Apply For A Full Title V Air Quality Permit As They Originally Proposed In Washington County [PaEN]

-- Environmental Integrity Project: DEP Made Changes To Permit For MarkWest Harmon Creek Natural Gas Processing Plant In Washington County To Reduce Air Emissions, Improve Accountability [PaEN]