An oil and gas company lost over a million gallons of drilling fluid into an abandoned coal mine in Washington County over a period of months, state records show.
Contractors for the pipeline company MarkWest Liberty Midstream & Resources LLC lost control of drilling fluid on at least 19 occasions over the fall and winter, according to Pennsylvania Department of Environmental Protection records. The records show that the company had similar experiences on two other pipelines it built in the area.
The fluid went into “a mine void” at the site of the abandoned Primrose Mine in Mount Pleasant Township during drilling for a new pipeline, the Chiarelli to Imperial Pipeline Project, between October and January. The mine was active in the early 1900s, according to state records.
The fluid is used to make drilling easier during horizontal directional drilling, a common technique used to bore holes underground for pipelines. The fluid, classified as industrial waste under state law, contained a mix of water, soda ash and bentonite clay, along with a product called Max Gel, according to DEP records. Max Gel is a silicone-based product used in drilling fluid. The company said in an email that the mixture is nontoxic and approved by the DEP, and that it’s monitoring for surface water contamination, but hasn’t found any.
The losses of fluid were first reported by PA Environment Digest, a website run by former DEP secretary David Hess.
Cat Lodge, who lives in nearby Robinson Township, doesn’t think the DEP should have allowed the company to keep drilling through the area of the abandoned mine. She’s worried about where the fluid ended up.
“Where did it go? And what do you do now if it winds up in somebody’s well water?” Lodge said. “I wouldn’t want this in my drinking water. I wouldn’t it in my animals’ drinking water. If it hits the waters of the Commonwealth, this could be hazardous to fish.”
The company told the DEP it did not contact local residents or test nearby groundwater.
Lodge, who works for the nonprofit Environmental Integrity Project, which is not involved in the case, thinks residents should know more about incidents like these.
“We need to know if something is in our water; if we’re exposed to something, we should know to protect ourselves,” Lodge said.
DEP spokeswoman Laina Aquiline said in an emailed statement that the agency “is continuing to investigate the reported loss of drilling fluids that occurred during horizontal directional drilling (HDD) activities associated with a MarkWest project. Because the investigation is ongoing, DEP cannot comment on potential future enforcement actions.”
Aquiline said MarkWest had “anticipated” the loss of drilling fluids into the mine “prior to commencing.”
“Currently, DEP has received no reports of drilling fluids reaching the surface, mine outfalls, or any local streams or water bodies,” Aquiline said.
“The material lost during the incident consists primarily of fresh water and bentonite clay. Any drilling fluid additives beyond water and bentonite must receive DEP approval prior to use.” Aquiline said MarkWest used soda ash and Max Gel as additives to their drilling fluid.
Aquiline said MarkWest engaged an independent third-party engineering firm to guide its response plan after the loss of fluids, as the company is required to do by state regulations.
The DEP’s publicly available records show the agency issued a notice of violation for the project for failing to report past losses, and could issue more, pending further investigation.
Editor’s Note: This story has been updated March 6, 2026 to include the use of Max Gel in the drilling fluid and comments by the DEP received after press time.
